Among women that experience hypertension in pregnancy, the recurrence rate in a next pregnancy is relatively low, and the course of disease is milder for most women with recurrent disease. These reassuring data should be used for shared decision-making in women who consider a new pregnancy after a pregnancy that was complicated by hypertension.

We found larger placentas and a higher placental weight/birthweight ratio among pregnancies conceived by ART compared with spontaneous pregnancies, and the difference was independent of length of gestation at delivery and ART method.

Both small and large placentas relative to birthweight were associated with fetal death in preterm births. At term, only small placentas relative to birthweight were associated with fetal death. Understanding the mechanisms behind the increased risk of adverse pregnancy outcomes in pregnancies with disproportionate placental weight/birthweight ratio may be important for prevention of fetal deaths.

In diabetic pregnancies, placental weight as well as placental weight relative to birthweight were higher than in non-diabetic pregnancies.

Please cite this paper as: Haavaldsen C, Samuelsen S, Eskild A. The association of maternal age with placental weight: a population‐based study of 536 954 pregnancies. BJOG 2011;118:1470–1476. Objective  To study the association of maternal age with placental weight, birthweight and placental weight/birthweight ratio. Design  Population‐based study. Setting  Medical Birth Registry of Norway. Population  All singleton births in Norway in the period 1999–2008 (n = 536 954). Methods  Z‐scores of placental weight and birthweight were calculated and divided into deciles. The proportions with a small or a large placenta were calculated within each maternal age group. Also, the odds ratios of having a small (lowest decile) and a large (highest decile) placenta, according to maternal age, were estimated, with and without adjustment for birthweight in grams, parity, smoking, pre‐eclampsia and diabetes. Main outcome measures  Placental weight, birthweight and placental weight/birthweight ratio. Results  The mean placental weight increased with maternal age: 647.1 g in women below the age of 20 years and 691.3 g in women aged 45 years or older. Among the oldest group of women (≥45 years) 15.8% of placentas were in the highest decile of placental weight z‐score, whereas this was true for just 7.0% of women below the age of 20 years (Wald test, P < 0.001). Using women younger than 20 years of age as a reference, the odds ratio for having a placenta in the highest decile of placental weight z‐score was 2.50 (95% CI 1.92–3.26) for women aged 45 years or older, after adjustment for offspring birthweight, parity, maternal smoking, pre‐eclampsia and diabetes. Conclusion  We found an association between increased placental weight and maternal age, and this finding may be important in understanding the causes of adverse events associated with high maternal age.

Placental weight and placental weight to birthweight ratio were higher in pregnancies with infant Apgar score ≤7 compared with Apgar score >7.

Background Pre-eclampsia is a leading cause of maternal and perinatal mortality and morbidity. Early identification of women at risk during pregnancy is required to plan management. Although there are many published prediction models for pre-eclampsia, few have been validated in external data. Our objective was to externally validate published prediction models for pre-eclampsia using individual participant data (IPD) from UK studies, to evaluate whether any of the models can accurately predict the condition when used within the UK healthcare setting. Methods IPD from 11 UK cohort studies (217,415 pregnant women) within the International Prediction of Pregnancy Complications (IPPIC) pre-eclampsia network contributed to external validation of published prediction models, identified by systematic review. Cohorts that measured all predictor variables in at least one of the identified models and reported pre-eclampsia as an outcome were included for validation. We reported the model predictive performance as discrimination (C-statistic), calibration (calibration plots, calibration slope, calibration-in-the-large), and net benefit. Performance measures were estimated separately in each available study and then, where possible, combined across studies in a random-effects meta-analysis. Results Of 131 published models, 67 provided the full model equation and 24 could be validated in 11 UK cohorts. Most of the models showed modest discrimination with summary C-statistics between 0.6 and 0.7. The calibration of the predicted compared to observed risk was generally poor for most models with observed calibration slopes less than 1, indicating that predictions were generally too extreme, although confidence intervals were wide. There was large between-study heterogeneity in each model’s calibration-in-the-large, suggesting poor calibration of the predicted overall risk across populations. In a subset of models, the net benefit of using the models to inform clinical decisions appeared small and limited to probability thresholds between 5 and 7%. Conclusions The evaluated models had modest predictive performance, with key limitations such as poor calibration (likely due to overfitting in the original development datasets), substantial heterogeneity, and small net benefit across settings. The evidence to support the use of these prediction models for pre-eclampsia in clinical decision-making is limited. Any models that we could not validate should be examined in terms of their predictive performance, net benefit, and heterogeneity across multiple UK settings before consideration for use in practice. Trial registration PROSPERO ID: CRD42015029349.

BackgroundWe studied associations of number of daily cigarettes in the first trimester with placental weight and birthweight in women who smoked throughout pregnancy, and in women who stopped smoking after the first trimester.MethodsWe included all women with delivery of a singleton in Norway (n = 698 891) during 1999–2014, by using data from the Medical Birth Registry of Norway. We assessed dose-response associations by applying linear regression with restricted cubic splines.ResultsIn total, 12.6% smoked daily in the first trimester, and 3.7% stopped daily smoking. In women who smoked throughout pregnancy, placental weight and birthweight decreased by number of cigarettes; however, above 11–12 cigarettes we estimated no further decrease (Pnon-linearity < 0.001). Maximum decrease in placental weight in smokers compared with non-smokers was 18.2 g [95% confidence interval (CI): 16.6 to 19.7], and for birthweight the maximum decrease was 261.9 g (95% CI: 256.1 to 267.7). In women who stopped smoking, placental weight was higher than in non-smokers and increased by number of cigarettes to a maximum of 16.2 g (95% CI: 9.9 to 22.6). Birthweight was similar in women who stopped smoking and non-smokers, and we found no change by number of cigarettes (Pnon-linearity < 0.001).ConclusionsIn women who smoked throughout pregnancy, placental weight and birthweight decreased non-linearly by number of cigarettes in the first trimester. In women who stopped smoking, placental weight was higher than in non-smokers and increased linearly by number of cigarettes; birthweight was almost similar to that of non-smokers.