Dating of Pregnancy in First versus Second Trimester in Relation to Post-Term Birth Rate: A Cohort Study

The association of placental to fetal ratio with pregnancy duration

INTRODUCTION

Our objective was to study the association of placental size, fetal size, and placental size relative to fetal size (placental to fetal ratio) at gestational week 27 with time to spontaneous delivery.

MATERIAL AND METHODS

We included 100 pregnancies in a follow-up study from gestational week 27 until spontaneous delivery. Placental and fetal volume (in cm3) were measured at gestational week 27 by magnetic resonance imaging (MRI), and the association of placental to fetal ratio (placental volume/fetal volume) with delivery after spontaneous onset of labor was estimated as hazard ratios (HR) by applying Cox regression models. Pregnancies with deliveries after planned cesarean section or induction of labor provided follow-up time until these events. An HR lower than 1.0 indicates decreased risk of spontaneous delivery.

RESULTS

Mean placental volume was 532 cm3 (SD 136 cm3) at gestational week 27, and fetal volume was 961 cm3 (SD 112 cm3). This yielded a mean placental to fetal ratio of 0.55 (SD 0.12). The HR of spontaneous delivery decreased with increasing placental to fetal ratio (HR 0.013 (95% CI: 0.001-0.121), Wald statistic 14.704 (p < 0.001)), indicating a longer duration of pregnancy with a higher placental to fetal ratio at gestational week 27. The HR of spontaneous delivery also decreased with increasing placental size, but the association was less prominent than the HR associated with placental to fetal ratio (HR 0.997 [95% CI: 0.995-0.999], Wald statistic 7.638 [p = 0.006]). We estimated no association with fetal size (HR 1.001 [95% CI 0.999-1.003], Wald statistic 1.728 [p = 0.189]).

CONCLUSIONS

Our findings suggest that the placental to fetal ratio at gestational week 27 may be an indicator of the remaining duration of pregnancy until the onset of spontaneous labor.

Biparietal diameter for first-trimester pregnancy dating: multicenter cohort study

OBJECTIVE

To evaluate the accuracy of fetal biparietal diameter (BPD) measurement in comparison with crown-rump length (CRL) measurement for pregnancy dating at 11-13 weeks' gestation.

METHODS

This was a retrospective multicenter cohort study performed in five maternity units in Spain, the UK, Belgium and Bulgaria between January 2011 and December 2019. We included all women who attended a routine ultrasound examination at 11 + 0 to 13 + 6 weeks who had a singleton pregnancy with a viable non-malformed fetus/neonate and ultrasound-derived measurements for both CRL and BPD, along with a comprehensive record of pregnancy outcomes. We developed a formula for pregnancy dating based on BPD using data from pregnancies conceived via in-vitro fertilization (IVF) by applying a simple linear regression. We validated this formula both internally and externally and compared it with the most commonly used formulae (Robinson's CRL-based and Kustermann's BPD-based formulae) through utilization of the Euclidean distance, relative absolute error and mean squared error. We also examined the rate of induction of labor for post-term pregnancy based on dating using each of the formulae.

RESULTS

A total of 49 492 women were included in the study, comprising 47 223 (95.4%) who conceived spontaneously and 2269 (4.6%) who conceived via IVF. In the internal validation performed using data from IVF pregnancies, our newly developed formula showed no significant difference when compared with the true gestational age calculated using conception date, with a mean difference of 0.0006 (95% CI, -0.09 to 0.09) days. In contrast, the mean difference of Kustermann's BPD-based formula was -0.31 (95% CI, -0.46 to -0.17) days and the mean difference of Robinson's CRL-based formula was -1.78 (95% CI, -1.88 to -1.68) days. In the external validation using data from spontaneously conceived pregnancies, with dating using Robinson's formula as the reference for 'true' gestational age, both our formula and Kustermann's formula resulted in underestimation of gestational age, with significant mean differences of -1.25 (95% CI, -1.28 to -1.22) days and -0.96 (95% CI, -0.98 to -0.93) days, respectively. The largest differences compared with Robinson's formula-based dating results were observed between 11 + 0 and 12 + 0 weeks. Dating the pregnancy using Robinson's formula led to 8.1% of pregnancies identified as requiring induction after 41 + 3 weeks, compared with 6.8% (P < 0.001) and 7.0% (P < 0.001) when applying our formula and Kustermann's formula, respectively.

CONCLUSION

Pregnancy dating based on ultrasound measurement of fetal BPD between 11 + 0 and 13 + 6 weeks' gestation is a reliable alternative to dating based on fetal CRL. © 2025 International Society of Ultrasound in Obstetrics and Gynecology.

Perinatal death in the Nordic countries in relation to gestational age: The impact of registration practice

INTRODUCTION

Although perinatal death rates in the Nordic countries are among the lowest in the world, the risk of perinatal death is unevenly distributed across the Nordic countries, despite similarity in health care systems and pregnancy care. Birth registration practices across countries may explain some of the differences. We investigated differences in national registration of perinatal mortality within the Nordic countries and its impact on perinatal mortality according to gestational age.

MATERIAL AND METHODS

Each country provided information by answering a questionnaire about registration of perinatal deaths. Furthermore, we collected aggregated count data based on Medical Birth Registries (MBR) from all Nordic countries in 2000 to 2021. Perinatal mortality was defined as stillbirth or neonatal death occurring within first 7 days of life. Data were grouped into six groups by gestational age (GA): extremely preterm (>28 + 0 weeks, subdivided into 22 + 0-23 + 6 and 24 + 0-27 + 6), very preterm (GA 28 + 0-31 + 6), moderate preterm (GA 32 + 0-33 + 6), late preterm (GA 34 + 0-36 + 6), term (GA 37 + 0-40 + 6) and late term or post-term birth (GA ≥ 41 + 0). Perinatal mortality rate and risk ratio with 95% confidence intervals were calculated per country for each gestational age group. For Denmark, separate analyses included and excluded induced abortions.

RESULTS

The study included 6 343 805 live births, 22 727 stillbirths and 8932 liveborn infants who died within the first week of life after GA 22 + 0. Further 25 057 births were included with GA < 22 + 0, unknown GA and as a result of induced abortion. Overall, perinatal mortality rates decreased during year 2000-2021 in all Nordic countries. After exclusion of induced abortions, the perinatal mortality rate was similar in the five Nordic countries. The perinatal mortality rate for extremely preterm born infants was highest in Denmark, whereas the highest rate among infants born late term/post-term was in Sweden.

CONCLUSIONS

The perinatal mortality rate in the Nordic countries is still decreasing, especially in the group of extremely preterm born infants. This study supports the need for further standardization of birth registration practices to ensure the validity of international comparisons.

Influence of different methods for calculating gestational age at birth on prematurity and small for gestational age proportions: a systematic review with meta-analysis

BACKGROUND

Recognizing premature newborns and small-for-gestational-age (SGA) is essential for providing care and supporting public policies. This systematic review aims to identify the influence of the last menstrual period (LMP) compared to ultrasonography (USG) before 24 weeks of gestation references on prematurity and SGA proportions at birth.

METHODS

Systematic review with meta-analysis followed the recommendations of the PRISMA Statement. PubMed, BVS, LILACS, Scopus-Elsevier, Embase-Elsevier, and Web-of-Science were searched (10-30-2022). The research question was: (P) newborns, (E) USG for estimating GA, (C) LMP for estimating GA, and (O) prematurity and SGA rates for both methods. Independent reviewers screened the articles and extracted the absolute number of preterm and SGA infants, reference standards, design, countries, and bias. Prematurity was birth before 37 weeks of gestation, and SGA was the birth weight below the p10 on the growth curve. The quality of the studies was assessed using the New-Castle-Ottawa Scale. The difference between proportions estimated the size effect in a meta-analysis of prevalence.

RESULTS

Among the 642 articles, 20 were included for data extraction and synthesis. The prematurity proportions ranged from 1.8 to 33.6% by USG and varied from 3.4 to 16.5% by the LMP. The pooled risk difference of prematurity proportions revealed an overestimation of the preterm birth of 2% in favor of LMP, with low certainty: 0.02 (95%CI: 0.01 to 0.03); I² 97%). Subgroup analysis of USG biometry (eight articles) showed homogeneity for a null risk difference between prematurity proportions when crown-rump length was the reference: 0.00 (95%CI: -0.001 to 0.000; I²: 0%); for biparietal diameter, risk difference was 0.00 (95%CI: -0.001 to 0.000; I²: 41%). Only one report showed the SGA proportions of 32% by the USG and 38% by the LMP.

CONCLUSIONS

LMP-based GA, compared to a USG reference, has little or no effect on prematurity proportions considering the high heterogeneity among studies. Few data (one study) remained unclear the influence of such references on SGA proportions. Results reinforced the importance of qualified GA to mitigate the impact on perinatal statistics.

TRIAL REGISTRATION

Registration number PROSPERO: CRD42020184646.

Development and Validation of a Nomogram to Estimate Risk of Cesarean After Induction of Labor in Term Pregnancies with an Unfavorable Cervix in Iran

This study aimed to develop and validate a labor induction nomogram for nulliparous and multiparous women who were 38 weeks pregnant or more and had their labor induced by an unfavorable cervix. This prospective study was conducted on 300 individuals (200 for nomogram development and 100 for nomogram validation). Height, body mass index at delivery, parity, gestational age, adjusted bishop score, and cesarean section risk assessment were all recorded on a checklist. Participants were followed until they gave birth, and the type of delivery was noted in the checklist. Out of 300 labor inductions, 80 (26.7%) underwent a cesarean section. Cesarean risk estimation was the only predictor of delivery type based on multivariate logistic regression. The AUC (Area Under the Curve) in development group was 0.68 and in validation group was 0.71. The developed nomogram for predicting of cesarean section risk following labor induction has a relatively good predictive value among women.

Swedish intrauterine growth reference ranges of biometric measurements of fetal head, abdomen and femur

Ultrasonic assessment of fetal growth is an important part of obstetric care to prevent adverse pregnancy outcome. However, lack of reliable reference ranges is a major barrier for accurate interpretation of the examinations. The aim of this study was to create updated Swedish national reference ranges for intrauterine size and growth of the fetal head, abdomen and femur from gestational week 12 to 42. This prospective longitudinal multicentre study included 583 healthy pregnant women with low risk of aberrant fetal growth. Each woman was examined up to five times with ultrasound from gestational week 12 + 3 to 41 + 6. The assessed intrauterine fetal biometric measurements were biparietal diameter (outer–inner), head circumference, mean abdominal diameter, abdominal circumference and femur length. A two-level hierarchical regression model was employed to account for the individual measurements of the fetus and the number of repeated visits for measurements while accounting for the random effect of the identified parameterization of gestational age. The expected median and variance, expressed in both standard deviations and percentiles, for each individual biometric measurement was calculated. The presented national reference ranges can be used for assessment of intrauterine size and growth of the fetal head, abdomen and femur in the second and third trimester of pregnancy.

Adherence to Swedish national pregnancy dating guidelines and management of discrepancies between pregnancy dating methods: a survey study

Background

Swedish national guidelines for pregnancy dating were published in 2010. Follow-up is needed to assess adherence and to identify whether any clinical topics are not covered in the guidelines.

Methods

All units in Sweden that performed ultrasound-based pregnancy dating were asked to complete a web-based questionnaire comprising multiple-response questions and commentary fields. Information was collected regarding baseline information, current and previous clinical practice, and management of discrepancies between last-menstrual-period- and ultrasound-based methods for pregnancy dating.

Results

The response rate was 79%. Half of the units offered first-trimester ultrasound to all pregnant women. However, contrary to the guidelines, the crown–rump length was not used for ultrasound-based pregnancy dating in most units. Instead, ultrasound-based pregnancy dating was performed only if the biparietal diameter was between 21 and 55 mm. Management of discrepancies between methods for pregnancy dating varied widely.

Conclusions

The units reported high adherence to national guidelines, except for early pregnancy dating, for which many units followed unwritten or informal guidelines. The management of discrepancies between last-menstrual-period-based and ultrasound-based estimated day of delivery varied widely. These findings emphasize the need for regular updating of national written guidelines and efforts to improve their implementation in all units.

Leptin and Adiponectin as markers for preeclampsia in obese pregnant women, a cohort study

OBJECTIVE

Preeclampsia (PE) is a serious complication of pregnancy, the pathogenesis of which is largely unknown. We hypothesize that adipocytokines may play a role in the pathogenesis of PE, particularly in obese women, and evaluate leptin and adiponectin as potential first trimester markers for predicting PE.

STUDY DESIGN

A cohort of 2503 pregnancies, containing 93 PE pregnancies, was divided into women with normal weight, moderate, or severe obesity. All pregnancies had serum adiponectin and leptin measured in first trimester. Logistic regression was used to model PE with maternal characteristics and concentrations of the biomarkers.

RESULTS

In obese women a lower concentration of adiponectin was found in PE pregnancies; the concentration was lowest in the severely obese (p = 0.005). No association was found in normal weight women (p = 0.72). Leptin concentration had no association with PE in normal weight and moderately obese (p = 0.175-0.072), however in women with severe obesity a lower level of leptin was found (p = 0.049). The AUC was 0.73 for the ROC curve of combined maternal characteristics and adiponectin. Using adiponectin in women with moderate to severe obesity the sensitivity was 72.9% and the specificity was 49%.

CONCLUSIONS

In severely obese women, PE is associated with low serum adiponectin and leptin concentrations in first trimester. This indicates that the inability of adipokine regulation to adapt to severe obesity may play a role in the pathogenesis of PE. Adipocytokines may contribute in identification of risk pregnancies among severe obese.

The effect of obesity on early fetal growth and pregnancy duration: a cohort study

OBJECTIVE

The objective of this study is to investigate the effect of maternal obesity on fetal size in first- and second-trimester pregnancies and to determine duration of pregnancy as estimated by a variety of methods.

METHODS

Between 2006 and 2011, a cohort study included (n = 9055) singleton pregnancies that resulted in live birth at Holbaek Hospital in Denmark. This study recorded first- and second-trimester fetal measurements and maternal anthropometry. Characteristics considered included mother's age, parity, height, body mass index (BMI), smoking habits, and sex of child. The correlation between BMI and duration of pregnancy was analyzed by time-to-event analysis and accounted for medical intervention by censoring while correlation of BMI on fetal size was evaluated by multiple regression analysis.

RESULTS

Adjusting for maternal and fetal characteristics, BMI was associated with prolonged pregnancy duration (0.20-0.22 d per kg/m² (standard error (SE) 0.02)) when using ultrasound and 0.26 d per kg/m² (SE: 0.03) when using last menstrual period. With increasing BMI, fetal biometries in first and second trimester were significantly smaller than expected (0.08 mm per kg/m² when measured by crown rump length (SE 0.02)).

CONCLUSIONS

Maternal BMI is correlated to smaller fetal size in early pregnancy and prolongs duration of pregnancy.