Early pregnancy loss incidence in high-income settings: a protocol for a systematic review and meta-analysis

BACKGROUND

Early pregnancy loss (unintended pregnancy loss before 20 completed weeks of gestation) is a common adverse pregnancy outcome, with previous evidence reporting incidence ranging from 10 to 30% of detected pregnancies. The objective of this systematic review and meta-analysis is to determine the incidence and range of early pregnancy loss in contemporary pregnant populations based on studies with good internal and external validity. Findings may be useful for clinical counseling in pre-conception and family planning settings and for people who experience early pregnancy loss.

METHODS

We will search MEDLINE, EMBASE, and CINAHL databases using combinations of medical subject headings and keywords. Peer-reviewed, full-text original research articles that meet the following criteria will be included: (1) human study; (2) study designs: controlled clinical trials or observational studies with at least 100 pregnancies in the denominator, or systematic reviews of studies using these designs; (3) conducted in high-income countries; (4) reporting early pregnancy loss incidence, defined as unintended early pregnancy loss occurring prior to 20 weeks' gestation expressed as the number of losses among all pregnancies in the study period; (5) among a contemporary (1990 or later) general population of pregnancies; and (6) published between January 1, 1990, and August 31, 2021. We will assess the quality of included studies according to the United States Preventive Services Task Force Criteria for Assessing Internal and External Validity of Individual Studies. If appropriate, based on methodological comparability across included studies, we will conduct meta-analyses using random effects models to estimate the pooled incidence of early pregnancy loss among all studies with both good internal and external validity, with meta-analyses stratified by study design type (survey-based or self-reported and medical record-based), by induced abortion restrictions (restricted vs. unrestricted), and by gestational age (first trimester only vs. all gestational ages before 20 weeks).

DISCUSSION

This systematic review will synthesize existing evidence to calculate a current estimate of early pregnancy loss incidence and variability in reported incidence estimates in high-income settings. The findings of this review may inform updates to clinical counseling in pre-conception and family planning settings, as well as for patients experiencing early pregnancy loss.

SYSTEMATIC REVIEW REGISTRATION

We have registered this review with the International Prospective Register of Systematic Reviews (PROSPERO #226267 ).

Inter-hospital variation in use of obstetrical blood transfusion: a population-based cohort study

OBJECTIVE

To identify the extent of hospital-to-hospital variation in use of obstetrical blood transfusion.

DESIGN

Population-based cohort study linking provincial perinatal and blood transfusion registries.

SETTING

British Columbia, Canada, 2004-2015.

POPULATION

All pregnant women delivering at or beyond 20 weeks' gestation at any British Columbia hospital.

METHODS

Mixed-effects regression models were used to estimate hospital-specific transfusion rates after sequentially accounting for (1) the role of random variation, (2) maternal medical and obstetrical characteristics (i.e. patient case mix) and (3) institutional and delivery factors (such as use of instrumental or caesarean delivery).

MAIN OUTCOME MEASURES

Hospital-specific use of obstetrical red blood cell transfusion.

RESULTS

Among 44 hospitals, crude institutional transfusion rates across the study period ranged from 3.7 to 23.6 per 1000, with an average of 8.3 per 1000. After adjusting for maternal characteristics, institution and delivery risk factors, a nearly three-fold difference in rates between the 10th and 90th percentile remained (5.4-14.5 per 1000). Twelve sites had rates significantly higher or lower than the provincial average. Women residing in remote areas were 2.5-fold (95% CI 1.8-3.5] more likely to receive a blood transfusion than were women residing in metropolitan areas.

CONCLUSIONS

Meaningful variation between hospitals in use of blood transfusion during pregnancy was not explained by differences in patient case-mix or institutional factors, suggesting that over- or under-utilisation of this resource may be occurring in obstetrical care.

TWEETABLE ABSTRACT

Use of blood transfusion in pregnant women varied broadly between hospitals in British Columbia, Canada.

Pregnancy weight gain by gestational age and stillbirth: a population-based cohort study

Objective

To study the association between total and early pregnancy (<22 completed weeks) weight gain and risk of stillbirth, stratified by early‐pregnancy body mass index (BMI).

Design

Population‐based cohort study.

Setting

Stockholm‐Gotland Region, Sweden.

Population

Pregnant women with singleton births (n = 160 560).

Methods

Pregnancy weight gain was standardised into gestational age‐specific z‐scores. For analyses of total pregnancy weight gain, a matched design with an incidence density sampling approach was used. Findings were also contrasted with current Institute of Medicine (IOM) weight gain recommendations.

Main outcome measures

Stillbirth defined as fetal death at ≥22 completed weeks of gestation.

Results

For all BMI categories, there was no statistical association between total or early pregnancy weight gain and stillbirth within the range of a weight gain z‐score of −2.0 SD to +2.0 SD. Among normal‐weight women, the adjusted odds ratio of stillbirth for lower (−2.0 to −1.0 SD) and higher (+1.0 to +1.9 SD) total weight gain was 0.85 (95% CI; 0.48–1.49) and 1.03 (0.60–1.77), respectively, as compared with the reference category. Further, there were no associations between total or early pregnancy weight gain and stillbirth within the range of weight gain currently recommended by the IOM. For the majority of the BMI categories, the point estimates at the extremes of weight gain values (<−2.0SD and ≥2.0 SD) suggested protective effects of low weight gain and increased risks of high weight gain, but estimates were imprecise and not statistically significant.

Conclusion

We found no associations between total or early pregnancy weight gain and stillbirth across the range of weight gain experienced by most women.

Tweetable abstract

There was no association between weight gain during pregnancy and stillbirth among most women.

Tweetable abstract

There was no association between weight gain during pregnancy and stillbirth among most women.

Gestational weight gain, prepregnancy body mass index and offspring attention-deficit hyperactivity disorder symptoms and behaviour at age 10

OBJECTIVE

To assess offspring attention-deficit hyperactivity disorder (ADHD) symptoms and emotional/behavioural impairments at age 10 years in relation to maternal gestational weight gain (GWG) and prepregnancy body mass index (BMI).

DESIGN AND SETTING

Longitudinal birth cohort from Magee-Womens Hospital, Pittsburgh, Pennsylvania (enrolled 1983-86).

POPULATION

Mother-infant dyads (n = 511) were followed through pregnancy to 10 years.

METHODS

Self-reported total GWG was converted to gestational-age-standardised z-scores. Multivariable linear and negative binomial regressions were used to estimate effects of GWG and BMI on outcomes.

MAIN OUTCOME MEASURES

Child ADHD symptoms were assessed with the Conners' Continuous Performance Test. Child behaviour was assessed by parent and teacher ratings on the Child Behaviour Checklist (CBCL) and Teacher Report Form, respectively.

RESULTS

The mean (SD) total GWG (kg) was 14.5 (5.9), and 10% of women had a pregravid BMI ≥30 kg/m² . Prepregnancy obesity (BMI of 30 kg/m² ) was associated with increased offspring problem behaviours including internalising behaviours (adjusted β 3.3 points, 95% CI 1.7-4.9), externalising behaviours (adjusted β 2.9 points, 95% CI 1.4-4.6), and attention problems (adjusted β 2.3 points, 95% CI 1.1-3.4) on the CBCL, compared with normal weight mothers (BMI of 22 kg/m² ). There were nonsignificant trends towards increased offspring impulsivity with low GWG among lean mothers (adjusted incidence rate ratio 1.2, 95% CI 0.9-1.5) and high GWG among overweight mothers (adjusted incidence rate ratio 1.7, 95% CI 0.9-2.8), but additional outcomes did not differ by GWG z-score. Results were not meaningfully different after excluding high-substance users.

CONCLUSIONS

In a low-income and high-risk sample, we observed a small increase in child behaviour problems among children of obese mothers, which could have an impact on child behaviour in the population.

TWEETABLE ABSTRACT

Maternal obesity is associated with a small increase in child behaviour problems.

Maternal and neonatal outcomes after implementation of a hospital policy to limit low-risk planned caesarean deliveries before 39 weeks of gestation: an interrupted time-series analysis

OBJECTIVE

To evaluate the extent to which implementing a hospital policy to limit planned caesarean deliveries before 39 weeks of gestation improved neonatal health, maternal health, and healthcare costs.

DESIGN

Retrospective cohort study.

SETTING

British Columbia Women's Hospital, Vancouver, Canada, in the period 2005-2012.

POPULATION

Women with a low-risk planned repeat caesarean delivery.

METHODS

An interrupted time series design was used to evaluate the policy to limit planned caesarean deliveries before 39 weeks of gestation, introduced on 1 April 2008.

MAIN OUTCOME MEASURES

Composite adverse neonatal health outcome (respiratory morbidity, 5-minute Apgar score of <7, neonatal intensive care unit admission, mortality), postpartum haemorrhage, obstetrical wound infection, out-of-hour deliveries, length of stay, and healthcare costs.

RESULTS

Between 2005 and 2008, 60% (1204/2021) of low-risk planned caesarean deliveries were performed before 39 weeks of gestation. After the introduction of the policy, the proportion of planned caesareans dropped by 20 percentage points (adjusted risk difference of 20 fewer cases per 100 deliveries; 95% CI -25.8, -14.3) to 41% (1033/2518). The policy had no detectable impact on adverse neonatal outcomes (2.2 excess cases per 100; 95% CI -0.4, 4.8), maternal complications, or healthcare costs, but increased the risk of out-of-hours delivery from 16.2 to 21.1% (adjusted risk difference 6.3 per 100; 95% CI 1.6, 10.9).

CONCLUSIONS

We found little evidence that a hospital policy to limit planned caesareans before 39 weeks of gestation reduced adverse neonatal outcomes. Hospital administrators intending to introduce such policies should anticipate, and plan for, modest increases in out-of-hours and emergency-timing.

Using inter-institutional practice variation to understand the risks and benefits of routine labour induction at 41(+0) weeks

OBJECTIVE

To evaluate the risks and benefits of routine labour induction at 41(+0) weeks' gestation for mother and newborn.

DESIGN

Population-based retrospective cohort study of inter-institutional variation in labour induction practices for women at or beyond 41(+0) weeks' gestation.

POPULATION

Women in British Columbia, Canada, who remained pregnant ≥41(+0) weeks and delivered at one of the province's 42 hospitals with >50 annual deliveries, 2008-2012 (n = 14,627).

METHODS

The proportion of women remaining pregnant a week or more past the expected delivery date who were induced at 41(+0) or 41(+1) weeks' gestation for an indication of 'post-dates' was calculated for each institution. We used instrumental variable analysis (using the institutional rate of labour induction at 41(+0) weeks as the instrument) to estimate the effect of labour induction on maternal and neonatal health outcomes.

MAIN OUTCOME MEASURES

Caesarean delivery, instrumental delivery, post-partum haemorrhage, 3rd or 4th degree lacerations, macrosomia, neonatal intensive care unit admission, and 5-minute Apgar score <7.

RESULTS

Institutional rates of labour induction at 41(+0) weeks ranged from 14.3 to 46%. Institutions with higher (≥30%) and average (20-29.9%) induction rates did not have significantly different rates of caesarean delivery, instrumental delivery, or other maternal or neonatal outcomes than institutions with lower induction rates (<20%). Instrumental variable analyses also demonstrated no significantly increased (or decreased) risk of caesarean delivery (0.69 excess cases per 100 pregnancies [95% CI -10.1, 11.5]), instrumental delivery (8.9 per 100 [95% CI -2.3, 20.2]), or other maternal or neonatal outcomes in women who were induced (versus not induced).

CONCLUSIONS

Within the current range of clinical practice, there was no evidence that differential use of routine induction at 41(+0) weeks affected maternal or neonatal health outcomes.

Gestational weight gain in twin pregnancies and maternal and child health: a systematic review

Our objective was to systematically review the data interrogating the association between gestational weight gain (GWG) and maternal and child health among women with twin gestations. We identified 15 articles of twin gestations that studied GWG in relation to a maternal, perinatal or child health outcome and controlled for gestational age at delivery and prepregnancy body mass index. A positive association between GWG and fetal size was consistently found. Evidence on preterm birth and pregnancy complications was inconsistent. The existing studies suffer from serious methodological weaknesses, including not properly accounting for the strong correlation between gestational duration and GWG and not controlling for chorionicity. In addition, serious perinatal outcomes were not studied, and no research is available on the association between GWG and outcomes beyond birth. Our systematic review underscores that GWG in twin gestations is a neglected area of research. Rigorous studies are needed to inform future evidence-based guidelines.

Epidemiological investigation of a temporal increase in atonic postpartum haemorrhage: a population-based retrospective cohort study

OBJECTIVE

Increases in atonic postpartum haemorrhage (PPH) have been reported from several countries in recent years. We attempted to determine the potential cause of the increase in atonic and severe atonic PPH.

DESIGN

Population-based retrospective cohort study.

SETTING

British Columbia, Canada, 2001-2009.

POPULATION

All women with live births or stillbirths.

METHODS

Detailed clinical information was obtained for 371 193 women from the British Columbia Perinatal Data Registry. Outcomes of interest were atonic PPH and severe atonic PPH (atonic PPH with blood transfusion ≥1 unit; atonic PPH with blood transfusion ≥3 units or procedures to control bleeding), whereas determinants studied included maternal characteristics (e.g. age, parity, and body mass index) and obstetrics practice factors (e.g. labour induction, augmentation, and caesarean delivery). Year-specific unadjusted and adjusted odds ratios for the outcomes were compared using logistic regression.

MAIN OUTCOME MEASURES

Atonic PPH and severe atonic PPH.

RESULTS

Atonic PPH increased from 4.8% in 2001 to 6.3% in 2009, atonic PPH with blood transfusion ≥1 unit increased from 16.6 in 2001 to 25.5 per 10 000 deliveries in 2009, and atonic PPH with blood transfusion ≥3 units or procedures to control bleeding increased from 11.9 to 17.6 per 10 000 deliveries. The crude 34% (95% CI 26-42%) increase in atonic PPH between 2001 and 2009 remained unchanged (42% increase, 95% CI 34-51%) after adjustment for determinants of PPH. Similarly, adjustment did not explain the increase in severe atonic PPH.

CONCLUSIONS

Changes in maternal characteristics and obstetric practice do not explain the recent increase in atonic and severe atonic PPH.

Timing of delivery for pregnancies with congenital diaphragmatic hernia

A recent report has suggested that delivery at early term ages may be associated with lower mortality among infants with congenital diaphragmatic hernia. We sought to confirm this finding by examining gestational age-specific mortality in the USA in term infants with isolated congenital diaphragmatic hernia, delivered following the spontaneous onset of labour. In the final population of 928 infants, neonatal and infant mortality decreased with advancing gestation, from 25 and 36% at 37 weeks of gestation, respectively, to 17 and 20% at 40 weeks of gestation, respectively. Log-binomial regression models showed that neonatal and infant mortality at 37 weeks of gestation were significantly higher than at 40 weeks. Further evidence, ideally from a randomised trial, is needed before recommendations for clinical practice on timing of delivery should be made.

Influence of ultrasound-to-delivery interval and maternal-fetal characteristics on validity of estimated fetal weight

OBJECTIVES

To explore the effects of ultrasound-to-delivery interval and maternal-fetal characteristics on the distribution of measurement error in estimated fetal weights (EFWs), and to determine the predictive ability of EFW for diagnosis of small-for-gestational age (SGA) and large-for-gestational age (LGA) among infants delivered within 1 day of an ultrasound examination.

METHODS

Percentage differences between EFW and birth weights were calculated in 3697 pregnancies. Linear regression was used to compare the accuracy of EFW for births on each of the 6 days after an ultrasound scan with the accuracy observed among births on the same day. The sensitivity, specificity, positive predictive value (PPV) and negative predictive value for diagnosis of SGA and LGA according to EFW was assessed.

RESULTS

The mean +/- SD percentage difference among deliveries within 1 day of the last ultrasound scan was 0.2 +/- 9.0%. Mean percentage differences were not significantly different from day 0 on days 1, 2 and 3; however, combining the data from these 4 days obscured a slight bias towards an overestimation of weight evident on day 0 and day 1. Among deliveries within 1 day of an ultrasound scan, the PPV was 61% for SGA diagnosis and 54% for LGA diagnosis.

CONCLUSION

Combining data from births > 1 day after the last ultrasound examination may lead to a false conclusion that there is systematic underestimation of weight. EFW tended to underestimate the weight of macrosomic fetuses and overestimate that of small fetuses which limited sensitivity and PPV. Maternal-fetal characteristics are weak predictors of individual errors in EFW.