Society for Maternal-Fetal Medicine Consult Series #50: The role of activity restriction in obstetric management: (Replaces Consult Number 33, August 2014)

Prediction and prevention of preterm birth: Quality assessment and systematic review of clinical practice guidelines using the AGREE II framework

BACKGROUND

Prediction of pregnancies at risk of preterm birth (PTB) may allow targeted prevention strategies.

OBJECTIVES

To assess quality of clinical practice guidelines (CPGs) and identify areas of agreement and contention in prediction and prevention of spontaneous PTB.

SEARCH STRATEGY

We searched for CPGs regarding PTB prediction and prevention in asymptomatic singleton pregnancies without language restriction in January 2024.

SELECTION CRITERIA

CPGs included were published between July 2017 and December 2023 and contained statements intended to direct clinical practice.

DATA COLLECTION AND ANALYSIS

CPG quality was assessed using the AGREE-II tool. Recommendations were extracted and grouped under domains of prediction and prevention, in general populations and high-risk groups.

MAIN RESULTS

We included 37 CPGs from 20 organizations; all were of moderate or high quality overall. There was consensus in prediction of PTB by identification of risk factors and cervical length screening in high-risk pregnancies and prevention of PTB by universal screening and treatment for asymptomatic bacteriuria, screening and treatment for BV in high-risk pregnancies, and use of preventative progesterone and cerclage. Areas of contention or limited consensus were the role of PTB clinics, universal cervical length measurement, biomarkers and cervical pessaries.

CONCLUSIONS

This review identified strengths and limitations of current PTB CPGs, and areas for future research.

Physical Activity in Work and Leisure Time during Pregnancy, and Its Influence on Maternal Health and Perinatal Outcomes

BACKGROUND

Physical inactivity during pregnancy has been shown to be linked to an increased risk of complications. However, during pregnancy, doubts arise about what type, intensity and frequency of physical activity are most recommended.

OBJECTIVE

Our main objective was to know the level of physical activity (PA) and sedentary lifestyle in a representative sample of pregnant women in Málaga, one of the most populated cities in Spain. Also, we aimed to find out the effects of PA on obstetric and perinatal outcomes and on the mental health of pregnant women, differentiated according to PA intensity and domain.

METHODS

Five hundred and forty full-term pregnant women who had their obstetric checks in the maternity ward of the Regional University Hospital of Málaga were recruited through consecutive sampling. Participants answered a questionnaire that included the WHO Global Physical Activity Questionnaire (GPAQ), the Edinburgh Depression Scale (EDS), the Generalized Anxiety Disorder Scale (GAD-7) and some other sociodemographic and health-related questions. Subsequently, information about perinatal outcomes was obtained after birth.

RESULTS

Only 50.8% of women followed the WHO recommendations on activity. We found a high proportion of obese pregnant women and a direct effect of a sedentary lifestyle on the rate of cesarean sections and vulvovaginal tears in spontaneous births, as well as on the mental health of future mothers. Women's age, the number of children, BMI at the beginning of pregnancy and leisure time physical activity (LTPA) explained anxiety scores, and age, LTPA, BMI at the end of pregnancy and intense work-related physical activity (WTPA) predicted depression scores.

CONCLUSIONS

LTPA improves obstetric outcomes, helping to reduce the rate of cesarean sections and vulvovaginal tears, as well as reducing prenatal anxiety and depression.

Ambulation for latency during expectant management of preterm prelabor rupture of membranes: a randomized controlled trial (AMBLE)

BACKGROUND

Individuals hospitalized with preterm prelabor rupture of membranes are often advised to limit their activity or adhere to bed rest. Some evidence suggests that greater activity is associated with longer latency and improved outcomes, but no high-quality evidence from a randomized controlled trial exists.

OBJECTIVE

This study aimed to evaluate whether encouragement to ambulate at least 2000 steps daily affects latency among individuals with preterm prelabor rupture of membranes compared with usual care.

STUDY DESIGN

This was a multisite unblinded, 2-arm randomized trial of individuals at 23 0/7 to 35 0/7 weeks of gestation undergoing inpatient expectant management of preterm prelabor rupture of membranes with planned delivery at least 7 days away. Each participant wore a Fitbit Inspire that tracked steps. The intervention arm was encouraged (verbal and Fitbit-based reminders) to reach a goal of 2000 steps per day. The usual-care arm was allowed ad libitum activity with no step goal or reminders. The primary outcome was latency (days) from randomization to delivery. Secondary analyses included composite neonatal and maternal clinical outcomes and maternal mental health survey results. Statistical analyses were conducted with an intent-to-treat approach under a Bayesian framework using neutral priors (a priori assumed 50:50 likelihood of longer latency in either arm). A total of 100 participants were required to have 80% power to demonstrate a 4-day difference in latency with 75% certainty (Bayesian probability).

RESULTS

Among 163 eligible individuals, 100 (61%) were randomized, and after loss to follow-up, 95 were analyzed. Gestational age at randomization was 29 3/7 weeks (interquartile range, 26 2/7 to 31 5/7) in the intervention arm and 27 4/7 weeks (interquartile range, 25 4/7 to 29 6/7) in the usual-care arm. Median step counts were 1690 per day in the intervention arm (interquartile range, 1031-2641) and 1338 per day in the usual-care arm (interquartile range, 784-1913). Median days of latency were 9 days in the intervention arm (interquartile range, 4-17) and 6 days in the usual-care arm (interquartile range, 2-14). The primary analysis indicated a 65% posterior probability that the intervention increased latency relative to usual care (posterior relative risk, 1.09; 95% credible interval, 0.70-1.71). The relative risk was 0.55 (95% credible interval, 0.32-0.82) for the composite neonatal adverse outcome, with 99% posterior probability of intervention benefit, and was 0.94 (95% credible interval, 0.72-1.20) for the composite maternal adverse outcome, with 70% posterior probability of intervention benefit. There was a 94% posterior probability of the intervention arm having a greater decrease in maternal stress score from baseline to before delivery compared with the usual-care arm (mean arm difference, 3.24 points [95% credible interval, -7.23 to 0.79]). Adjustment for gestational age at randomization had minimal impact on secondary outcome results.

CONCLUSION

Individuals with preterm prelabor rupture of membranes randomized to encouragement to ambulate had a longer latency to delivery and improved neonatal and mental health outcomes, with similar maternal clinical outcomes compared with usual care.

Vasa Previa

Vasa previa refers to unprotected fetal vessels running through the membranes over the cervix. Until recently, this condition was associated with an exceedingly high perinatal mortality rate attributable to fetal exsanguination when the membranes ruptured. However, ultrasonography has made it possible to diagnose the condition prenatally, allowing cesarean delivery before labor or rupture of the membranes. Several recent studies have indicated excellent outcomes with prenatally diagnosed vasa previa. However, outcomes continue to be dismal when vasa previa is undiagnosed before labor. Risk factors for vasa previa include second-trimester placenta previa and low-lying placentas, velamentous cord insertion, placentas with accessory lobes, in vitro fertilization, and multifetal gestations. Recognition of individuals who are at risk and screening them will greatly decrease the mortality rate from this condition. Because of the relative rarity of vasa previa, there are no randomized controlled trials to guide management. Therefore, recommendations on the diagnosis and management of vasa previa are based largely on cohort studies and expert opinion. This Clinical Expert Series review addresses the epidemiology, pathophysiology, natural history, diagnosis and management of vasa previa, as well as innovative treatments for the condition.

The Contribution of Commonly Diagnosed Genetic Disorders to Small for Gestational Age Birth and Subsequent Morbidity and Mortality in Preterm Infants

Objective

Preterm infants born small, vs. appropriate for gestational age (SGA, AGA) are at greater risk for morbidity and mortality. The contribution of genetic disorders to preterm SGA birth, morbidity, and mortality is unknown. We sought to determine the association between genetic disorders and preterm SGA birth, and the association between genetic disorders and morbidity or mortality within preterm SGA infants. We hypothesized that genetic disorders were significantly associated with both.

Study Design

This was a retrospective multicenter cohort study of 409 339 infants, born 23-33 weeks' gestation between 2000 and 2020. The odds of preterm SGA (vs AGA) birth, and the odds of severe morbidity or mortality within SGA preterm infants were determined for infants with genetic disorders, after adjusting for known risk factors.

Results

Genetic disorders were present in 3.0 and 1.3% of SGA and AGA preterm infants respectively; genetic disorders conferred an aOR (95% CI) of 2.06 (1.92, 2.21) of SGA birth. Genetic disorders were present in 4.3 of preterm SGA infants with morbidity or mortality and 2.1% of preterm SGA infants that did not experience morbidity or mortality. Genetic disorders conferred an aOR (95% CI) of 2.12 (2.66, 3.08) of morbidity or mortality.

Conclusions

Genetic disorders are strongly associated with preterm SGA birth, morbidity, and mortality. Clinicians should consider genetic testing of preterm SGA infants, particularly in the setting of other comorbidities or anomalies. Prospective, genomic research is needed to clarify the contribution of genetic disorders to disease in this population.

Society for Maternal-Fetal Medicine Statement: Response to the Food and Drug Administration's withdrawal of 17-alpha hydroxyprogesterone caproate

On April 5, 2023, the US Food and Drug Administration withdrew the approval of 17-alpha hydroxyprogesterone caproate, effective immediately, because of the lack of evidence that it reduces the risk of recurrent spontaneous preterm birth. This decision withdraws approval for all formulations of 17-alpha hydroxyprogesterone caproate (both intramuscular and subcutaneous) and applies to both brand name (Makena) and generic versions of the medication. We agree with the Food and Drug Administration determination and discourage continued prescribing of 17-alpha hydroxyprogesterone caproate, including through compounding pharmacies. We do not recommend changing indications for cerclage, indications for vaginal progesterone in patients with a short cervix, or recommendations against activity restriction based on the Food and Drug Administration withdrawal of 17-alpha hydroxyprogesterone caproate from the market. We recommend that discussion of the use of vaginal progesterone for primary prevention of recurrent preterm birth without input of cervical length or in those with a cervical length of ≥25 mm includes a shared decision-making process, especially if a progesterone formulation for preterm birth prevention was received in a previous pregnancy. The Food and Drug Administration determined that it would be inappropriate to delay the effective date of the withdrawal to allow patients currently receiving 17-alpha hydroxyprogesterone caproate to finish treatment. We agree with the Food and Drug Administration that there is no evidence of benefit with continued treatment. Patients currently receiving 17-alpha hydroxyprogesterone caproate can be counseled that the Food and Drug Administration's Center for Drug Evaluation and Research has not identified evidence of harm from discontinuation before 37 weeks of gestation.

Prevention and Therapy of Preterm Birth. Guideline of the DGGG, OEGGG and SGGG (S2k Level, AWMF Registry Number 015/025, September 2022) - Part 2 with Recommendations on the Tertiary Prevention of Preterm Birth and on the Management of Preterm Premature Rupture of Membranes

Aim The revision of this guideline was coordinated by the German Society for Gynecology and Obstetrics (DGGG), the Austrian Society for Gynecology and Obstetrics (OEGGG) and the Swiss Society for Gynecology and Obstetrics (SGGG). The aim of the guideline is to improve the prediction, prevention and management of preterm birth based on evidence from the current literature, the experience of members of the guidelines commission, and the viewpoint of self-help organizations. Methods The members of the contributing professional societies and organizations developed recommendations and statements based on international literature. The recommendations and statements were presented and adopted using a formal process (structured consensus conferences with neutral moderation, written Delphi vote). Recommendations Part 2 of this short version of the guideline presents statements and recommendations on the tertiary prevention of preterm birth and the management of preterm premature rupture of membranes.

Adherence to recommended physical activity restrictions due to threatened preterm delivery - a descriptive multi-center study

BACKGROUND

Threatened preterm delivery is a serious obstetrical complication and has for decades been prescribed physical activity restrictions (AR). Adherence to the recommended level of physical AR is however unknown. This study aimed to assess the objectively measured different physical positions and activities of pregnant women recommended AR due to threatened preterm delivery complications, compared to a reference group of uncomplicated pregnant women without restrictions, and to explore if admission status influenced adherence to AR.

METHODS

A Danish descriptive, clinical multi-center study included singleton pregnancies between 22-33 gestational weeks admitted to an antenatal ward or during midwife consultations either prescribed AR due to threatened preterm delivery or uncomplicated controls without restrictions. For seven days participants wore two tri-axial accelerometric SENS® monitors. Accelerometric data included time spent in five different positions, activities, and step counts. At inclusion demographic and obstetric information was collected.

RESULTS

Seventy-two pregnant women participated; 31% were prescribed strict AR, 15% moderate, 3% light, 8% unspecified, and 43% had no AR. Strict AR participants rested in the supine/lateral position for 17.7 median hours/day (range:9.6-24.0); sat upright 4.9 h/day (0.11-11.7); took 1,520steps/day (20-5,482), and 64% were inpatients. Moderate AR participants rested in the supine/lateral position for 15.1 h/day (11.5-21.6); sat upright 5.6 h/day (2.0-9.3); took 3,310steps/day (467-6,968), and 64% were outpatients. Participants with no AR rested 10.5 h/day (6.3-15.4) in supine/lateral position; sat upright 7.6 h/day (0.1-11.4) and took 9,235steps/day (3,225-20,818). Compared to no restrictions, participants with strict or moderate AR spent significant more time in physical resting positions and took significant fewer mean steps. Among strict AR admission status did not alter time spent in the physical positions, nor the step count.

CONCLUSIONS

Overall, participants adhered highly to the recommended AR. However, discriminating between strict and moderate AR recommendations did not alter how physical resting positions and activities were carried out. The admission status did not influence how participants adhered to strict AR.

Patterns of Prenatal Care Delivery and Obstetric Outcomes before and during the COVID-19 Pandemic

OBJECTIVE

 Health care providers and health systems confronted new challenges to deliver timely, high-quality prenatal care during the coronavirus disease 2019 (COVID-19) pandemic as the pandemic raised concerns that care would be delayed or substantively changed. This study describes trends in prenatal care delivery in 2020 compared with 2018 to 2019 in a large, commercially insured population and investigates changes in obstetric care processes and outcomes.

STUDY DESIGN

 This retrospective cohort study uses de-identified administrative claims for commercially insured patients. Patients whose entire pregnancy took place from March 1 to December 31 in years 2018, 2019, and 2020 were included. Trends in prenatal care, including in-person, virtual, and emergency department visits, were evaluated, as were prenatal ultrasounds. The primary outcome was severe maternal morbidity (SMM). Secondary outcomes included preterm birth and stillbirth. To determine whether COVID-19 pandemic-related changes in prenatal care had an impact on maternal outcomes, we compared the outcome rates during the pandemic period in 2020 to equivalent periods in 2018 and 2019.

RESULTS

 In total, 35,112 patients were included in the study. There was a significant increase in the prevalence of telehealth visits, from 1.1 to 1.2% prior to the pandemic to 17.2% in 2020, as well as a significant decrease in patients who had at least one emergency department visit during 2020. Overall prenatal care and ultrasound utilization were unchanged. The rate of SMM across this period was stable (2.3-2.8%) with a statistically significant decrease in the preterm birth rate in 2020 (7.4%) compared with previous years (8.2-8.6%; p < 0.05) and an unchanged stillbirth rate was observed.

CONCLUSION

 At a time when many fields of health care were reshaped during the pandemic, these observations reveal considerable resiliency in both the processes and outcomes of obstetric care.

KEY POINTS

· Overall prenatal care and ultrasound were unchanged from 2018 to 2019 to 2020.. · There was a large increase in the prevalence of telehealth visits in 2020.. · There was no change in the rate of severe maternal morbidity or stillbirth in 2020 compared with 2018 to 2019..

Activity Restriction and Hospitalization in Pregnancy: Can Bed-Rest Exercise Prevent Deconditioning? A Narrative Review

Evidence suggests that exercise during pregnancy is beneficial to both parent and fetus. However, there are high-risk pregnancy conditions that may warrant hospitalization. In our narrative review, we first describe the clinical implications for activity restriction in pregnancy, the effects of hospitalization, and the impact of bed rest on non-pregnant individuals. We provide examples of a 30 min bed-rest exercise program for hospitalized pregnant patients using the principal of suggested frequency, intensity, time (duration) of activity, and type of activity (FITT) using a resistance tool while in bed. If the individual is able to ambulate, we recommend short walks around the ward. Every minute counts and activity should be incorporated into a program at least 3 times per week, or every day if possible. As in all exercise programs, motivation and accountability are essential. Flexibility in timing of the exercise intervention is important due to the scheduling of medical assessments that may occur throughout the day for these hospitalized patients. Evidence suggests that by improving physical and emotional health through a bed-rest exercise program during a hospitalized pregnancy may help the individual resume demanding daily activity in the postpartum period and improve quality of life once birth has occurred. More research is necessary to improve the health of those individuals who are hospitalized during pregnancy, with follow up and support into the postpartum period.

Quality Appraisal of Nutritional Guidelines to Prevent, Diagnose, and Treat Malnutrition in All Its Forms during Pregnancy

This work aimed to identify clinical practice guidelines (CPGs) that include recommendations for the prevention, diagnosis, and treatment of women’s malnutrition during pregnancy and to evaluate the quality of these guidelines using the Appraisal of Guidelines for Research and Evaluation (AGREE II) instrument. We conducted a literature review using PubMed and different websites from January 2009 to February 2021. The quality of the CPGs was independently assessed by reviewers using the AGREE II instrument, which defines guidelines scoring >70% in the overall assessment as “high quality”. The analysis included 43 guidelines. Among the main findings, we identified that only half of the CPGs (51.1%) obtained a final “high quality” evaluation. AGREE II results varied widely across domains and categories. The two domains that obtained the highest scores were scope and purpose with 88.3% (range 39 to 100%) and clarity of presentation with 87.2% (range 25 to 100%). Among the “high quality” CPGs, the best scores were achieved by the three guidelines published by the National Institute of Health and Care Excellence (NICE) and the World Health Organization (WHO). Due to the importance of maternal nutrition in pregnancy, it is essential to join forces to improve the quality of the guidelines, especially in CPGs that do not meet the reference standards for quality.

Ultrasonographic changes in quadriceps femoris thickness in women with normal pregnancy and women on bed rest for threatened preterm labor

This study aimed to evaluate the changes in quadriceps femoris muscle thickness during the pregnancy and postpartum periods and to elucidate the effect of bed rest for threatened preterm labor on muscle thickness. In 26 women with normal pregnancy, quadriceps femoris thickness was measured at 11-13, 26, 30, and 35 weeks' gestation, and at 3-5 days and 1 month postpartum using ultrasonography. In 15 pregnant women treated with bed rest for threatened premature labor, quadriceps femoris thickness was measured at 30 and 35 weeks' gestation and postpartum. In women with normal pregnancy, quadriceps femoris thickness increased, peaking at 35 weeks' gestation, followed by a postpartum decrease. In women on bed rest, quadriceps femoris thickness showed no significant change during the pregnancy and postpartum periods, and the muscle was significantly thinner at 35 weeks' gestation than that in women with normal pregnancy. In conclusion, a significant increase in quadriceps femoris muscle thickness during normal pregnancy was found using ultrasonography. Meanwhile, in pregnant women on bed rest treatment, the quadriceps femoris was significantly thinner in the late third trimester than that in normal pregnant women. Prolonged bed rest can affect normal changes in the quadriceps femoris muscle thickness during the pregnancy and postpartum periods.

Perinatal and 2-year neurodevelopmental outcome in late preterm fetal compromise: the TRUFFLE 2 randomised trial protocol

INTRODUCTION

Following the detection of fetal growth restriction, there is no consensus about the criteria that should trigger delivery in the late preterm period. The consequences of inappropriate early or late delivery are potentially important yet practice varies widely around the world, with abnormal findings from fetal heart rate monitoring invariably leading to delivery. Indices derived from fetal cerebral Doppler examination may guide such decisions although there are few studies in this area. We propose a randomised, controlled trial to establish the optimum method of timing delivery between 32 weeks and 36 weeks 6 days of gestation. We hypothesise that delivery on evidence of cerebral blood flow redistribution reduces a composite of perinatal poor outcome, death and short-term hypoxia-related morbidity, with no worsening of neurodevelopmental outcome at 2 years.

METHODS AND ANALYSIS

Women with non-anomalous singleton pregnancies 32+0 to 36+6 weeks of gestation in whom the estimated fetal weight or abdominal circumference is <10th percentile or has decreased by 50 percentiles since 18-32 weeks will be included for observational data collection. Participants will be randomised if cerebral blood flow redistribution is identified, based on umbilical to middle cerebral artery pulsatility index ratio values. Computerised cardiotocography (cCTG) must show normal fetal heart rate short term variation (≥4.5 msec) and absence of decelerations at randomisation. Randomisation will be 1:1 to immediate delivery or delayed delivery (based on cCTG abnormalities or other worsening fetal condition). The primary outcome is poor condition at birth and/or fetal or neonatal death and/or major neonatal morbidity, the secondary non-inferiority outcome is 2-year infant general health and neurodevelopmental outcome based on the Parent Report of Children's Abilities-Revised questionnaire.

ETHICS AND DISSEMINATION

The Study Coordination Centre has obtained approval from London-Riverside Research Ethics Committee (REC) and Health Regulatory Authority (HRA). Publication will be in line with NIHR Open Access policy.

TRIAL REGISTRATION NUMBER

Main sponsor: Imperial College London, Reference: 19QC5491. Funders: NIHR HTA, Reference: 127 976. Study coordination centre: Imperial College Healthcare NHS Trust, Du Cane Road, London, W12 0HS with Centre for Trials Research, College of Biomedical & Life Sciences, Cardiff University. IRAS Project ID: 266 400. REC reference: 20/LO/0031. ISRCTN registry: 76 016 200.

Activity restriction and preterm birth prevention

PURPOSE OF REVIEW

Since the 1900s, activity restriction (AR) has been widely prescribed as a strategy for preventing preterm birth (PTB). Over the past decade, the practice has been called into question as numerous studies have demonstrated that AR does not improve obstetrical and perinatal outcomes but does confer significant physical and psychological risks. The purpose of this review is to offer clinicians a summary of the latest data on the risks, benefits, and efficacy of AR for the prevention of PTB.

RECENT FINDINGS

Both retrospective and prospective studies have demonstrated that AR does not significantly prolong pregnancy including those with multiple gestations, short cervices, ruptured membranes, and increased body mass indexes. Several studies have also shown that physical activity during pregnancy is associated with a higher incidence of vaginal delivery, a lower incidence of gestational diabetes mellitus, and a lower incidence of hypertensive disorders without increasing the risk of adverse neonatal outcomes.

SUMMARY

The culmination of these data led to the Society for Maternal-Fetal Medicines' release of an updated committee recommendation in August of 2020; AR should not be routinely prescribed as a treatment to prevent PTB.

Special Considerations Regarding Antenatal Care and Pregnancy Complications in Dichorionic Twin Pregnancies

Twin pregnancies account for about 3.3% of all deliveries in the United States with the majority of them being dichorionic diamniotic (DCDA). Maternal physiological adaption in twin pregnancies is exaggerated and the rate of almost every maternal and fetal complication is higher when compared to singleton pregnancies. Therefore, twin pregnancies necessitate closer antenatal surveillance by care providers who are familiar with the specific challenges unique to these pregnancies, and there is evidence that following women with twins in a specialized twin clinic can result in improved obstetrical outcomes. The importance of the first antenatal visit in twin pregnancies cannot be over emphasized and should preferably take place early in gestation as it is the optimal period to correctly identify the number of fetuses and the type of placentation (chorionicity and amnionicity). This will allow the patients, families, and caregivers to make the appropriate modifications and to tailor an optimal antenatal follow-up plan. This plan should focus on general recommendations such as weight gain and level of activity, education regarding complications specific to twin pregnancies along with the relevant symptoms and indications to seek care, as well as on close maternal and fetal monitoring. In this review, we summarize available evidence and current guidelines regarding antenatal care in DCDA twin pregnancies.

Role of early management of hyperornithinaemia-hyperammonaemia-homocitrullinuria syndrome in pregnancy

Hyperornithinaemia-hyperammonaemia-homocitrullinuria (HHH) syndrome is a rare inherited metabolic disorder of the urea cycle. Few reports exist to guide practices during pregnancy and fetal delivery. Yet, with affected patients often surviving into reproductive age, appropriate management of the peripartum phase is essential to ensure positive maternal and fetal outcomes.

Reassuringly, the vast majority of offspring of parturients with HHH syndrome have normal developmental outcomes; yet as seen here, fetal growth restriction does appear more frequently. Furthermore, in addition to the absent fetal corpus callosum observed in this case, other fetal cerebral abnormalities, including speech delay and intellectual impairment, have been recognised.

Unregulated dietary intake is one proposed factor for the observed disruption in fetal growth and early cerebral development. These stipulations not only reinforce the importance of extensive planning and teamwork, but also demonstrate the importance of timely intervention by a metabolic dietician and dietary compliance in the early organogenesis stage of pregnancy.

Longitudinal ultrasonic dimensions and parametric solid models of the gravid uterus and cervix

Tissue mechanics is central to pregnancy, during which maternal anatomic structures undergo continuous remodeling to serve a dual function to first protect the fetus in utero while it develops and then facilitate its passage out. In this study of normal pregnancy using biomechanical solid modeling, we used standard clinical ultrasound images to obtain measurements of structural dimensions of the gravid uterus and cervix throughout gestation. 2-dimensional ultrasound images were acquired from the uterus and cervix in 30 pregnant subjects in supine and standing positions at four time points during pregnancy (8-14, 14-16, 22-24, and 32-34 weeks). Offline, three observers independently measured from the images of multiple anatomic regions. Statistical analysis was performed to evaluate inter-observer variance, as well as effect of gestational age, gravity, and parity on maternal geometry. A parametric solid model developed in the Solidworks computer aided design (CAD) software was used to convert ultrasonic measurements to a 3-dimensional solid computer model, from which estimates of uterine and cervical volumes were made. This parametric model was compared against previous 3-dimensional solid models derived from magnetic resonance frequency images in pregnancy. In brief, we found several anatomic measurements easily derived from standard clinical imaging are reproducible and reliable, and provide sufficient information to allow biomechanical solid modeling. This structural dataset is the first, to our knowledge, to provide key variables to enable future computational calculations of tissue stress and stretch in pregnancy, making it possible to characterize the biomechanical milieu of normal pregnancy. This vital dataset will be the foundation to understand how the uterus and cervix malfunction in pregnancy leading to adverse perinatal outcomes.