Birth Weight in Consecutive Pregnancies and Maternal Cardiovascular Disease Mortality Among Spontaneous and Iatrogenic Term Births: A Population-Based Cohort Study.

Knowledge on the association between offspring birth weight and long-term risk of maternal cardiovascular disease (CVD) mortality is often based on firstborn infants without consideration of women's consecutive births. We studied long-term CVD mortality according to offspring birth weight patterns among women with spontaneous and iatrogenic term deliveries in Norway (1967-2020). We constructed birth weight quartiles (Qs) by combining standardized birth weight with gestational age in quartiles (Q1, Q2/Q3, and Q4) for the women's first 2 births. Mortality was estimated using Cox regression and expressed as hazard ratios (HRs) with 95% confidence intervals (CIs). Changes in offspring birth weight quartiles were associated with long-term maternal CVD mortality. Compared with women who had 2 term infants in Q2/Q3, women with a first offspring in Q2/Q3 and a second in Q1 had higher mortality risk (HR = 1.33, 95% CI: 1.18, 1.50), while risk was lower if the second offspring was in Q4 (HR = 0.78, 95% CI: 0.67, 0.91). The risk increase associated with having a first infant in Q1 was eliminated if the second offspring was in Q4 (HR = 0.99, 95% CI: 0.75, 1.31). These patterns were similar for women with iatrogenic and spontaneous deliveries. Inclusion of information from subsequent births revealed heterogeneity in maternal CVD mortality which was not captured when using only information based on the first offspring.

The relationship between cesarean delivery and fecundability: a population-based cohort study.

BACKGROUND: Previous studies have found that women who undergo cesarean delivery have fewer pregnancies. Cesarean delivery is also more common among women with lower fecundability. The potential role of cesarean delivery in reduced fecundability is not known. OBJECTIVE: This study aimed to assess the bidirectional relationship between cesarean delivery and fecundability. STUDY DESIGN: This was a prospective cohort study based on data from the Norwegian Mother, Father, and Child Cohort study linked with the Medical Birth Registry of Norway. We estimated the fecundability ratio (per cycle probability of pregnancy) and relative risk of infertility (time to pregnancy ≥12 months) by mode of delivery in the previous delivery among 42,379 women. For the reverse association, we estimated the relative risk of having a cesarean delivery by fecundability (the number of cycles women needed to conceive) among 74,024 women. RESULTS: The proportion of women with infertility was 7.3% (2707/37,226) among women with a previous vaginal delivery and 9.9% (508/5153) among women with a previous cesarean delivery, yielding an adjusted relative risk of 1.21 (95% confidence interval, 1.10-1.33). Women with a previous cesarean delivery also had a lower fecundability ratio (0.90; 95% confidence interval, 0.88-0.93) than women with a previous vaginal delivery. When assessing the reverse association between fecundability and cesarean delivery, we found that women who did not conceive within 12 or more cycles had a higher risk for cesarean delivery (adjusted relative risk, 1.57; 95% confidence interval, 1.48-1.66) than women who conceived within the first 2 cycles. The associations remained after controlling for sociodemographic and clinical risk factors and were observed across parity groups. CONCLUSION: Among women with more than 1 child, those who had a previous cesarean delivery subsequently had a lower fecundability ratio and an increased infertility risk than those who had a vaginal delivery. However, women who needed a longer time to conceive were also more prone to be delivered by cesarean delivery, indicating a bidirectional relationship between cesarean delivery and fecundability. This could suggest a common underlying explanatory mechanism and that the surgical procedure itself may not or only partly directly influence fecundability.

Cesarean delivery in Norwegian nulliparous women with singleton cephalic term births, 1967-2020: a population-based study.

BACKGROUND: Nulliparous women contribute to increasing cesarean delivery in the Nordic countries and advanced maternal age has been suggested as responsible for rise in cesarean delivery rates in many developed countries. The aim was to describe changes in cesarean delivery rates among nulliparous women with singleton, cephalic, term births by change in sociodemographic factors across 50 years in Norway. METHODS: We used data from the Medical Birth Registry of Norway and included 1 067 356 women delivering their first, singleton, cephalic, term birth between 1967 and 2020. Cesarean delivery was described by maternal age (5-year groups), onset of labor (spontaneous, induced and pre-labor CD), and time periods: 1967-1982, 1983-1998 and 1999-2020. We combined women's age, onset of labor and time period into a compound variable, using women of 20-24 years, with spontaneous labor onset during 1967-1982 as reference. Multivariable regression models were used to estimate adjusted relative risk (ARR) of cesarean delivery with 95% confidence interval (CI). RESULTS: Overall cesarean delivery increased both in women with and without spontaneous onset of labor, with a slight decline in recent years. The increase was mainly found among women < 35 years while it was stable or decreased in women > = 35 years. In women with spontaneous onset of labor, the ARR of CD in women > = 40 years decreased from 14.2 (95% CI 12.4-16.3) in 1967-82 to 6.7 (95% CI 6.2-7.4) in 1999-2020 and from 7.0 (95% CI 6.4-7.8) to 5.0 (95% CI 4.7-5.2) in women aged 35-39 years, compared to the reference population. Despite the rise in induced onset of labor over time, the ARR of CD declined in induced women > = 40 years from 17.6 (95% CI 14.4-21.4) to 13.4 (95% CI 12.5-14.3) while it was stable in women 35-39 years. CONCLUSION: Despite growing number of Norwegian women having their first birth at a higher age, the increase in cesarean delivery was found among women < 35 years, while it was stable or decreased in older women. The increase in cesarean delivery cannot be solely explained by the shift to an older population of first-time mothers.