Fertility treatment increases the risk of preterm birth independent of multiple gestations

Maternal Age Differences in Interpregnancy Interval and Preterm Birth Associations Accounting for Multiple Epidemiologic Biases

BACKGROUND

People who recently gave birth are strongly advised to wait 6 months before attempting pregnancy. Interpregnancy intervals (IPI) of ≥ 18 months are considered optimal. Current guidance is not tailored based on maternal characteristics (e.g., age).

OBJECTIVES

We evaluated whether maternal age modifies IPI-preterm birth (PTB) associations.

METHODS

From a US retrospective cohort of multiparae (1997-2011), we categorised IPI: < 6, 6-11, 12-17, 18-23 (reference), 24-59 or ≥ 60 months. PTB occurred before 37 0/7 weeks' gestation. We estimated risk ratios (RR) between IPI and PTB using modified Poisson regression, adjusted for potential confounders and stratified by age at prior delivery: < 25 (n = 2484), 25-29 (n = 1626) or ≥ 30 (n = 1209) years. We conducted quantitative bias analysis to adjust for volunteer bias and dependent misclassification between IPI and gestational length (since both are calculated using the estimated start of pregnancy). We computed E-values when RR lower bounds of the 95% simulation intervals were > 1.00.

RESULTS

Estimates were imprecise due to small numbers. However, in terms of general patterns, PTB risk was highest with < 6 months IPI in all age groups (covariate-adjusted RR point estimates ≥ 1.30). The strongest associations were observed among 25-29 years. For ≥ 30 years, PTB risk was lowest with 6-17 months IPI. After multiple bias adjustments, estimates tended to move downward, but similar patterns remained. For 25-29 years, the lower bound of the 95% simulation interval for < 6 versus 18-23 months IPI was > 1.00, with an E-value of 3.82, suggesting unmeasured confounding would need to be very strong to explain the association.

CONCLUSIONS

Estimates were imprecise. However, our study adds to growing evidence that IPI associations may be weaker among older individuals. Older individuals with shorter IPI may have lower PTB risk than those with currently recommended IPI, but more research is needed.

National-level assessment of gestational carrier pregnancies in the United States

PURPOSE

To assess national trends, characteristics, and delivery outcomes associated with gestational carriers (GC) pregnancies.

METHODS

This cross-sectional study queried the Healthcare Cost and Utilization Project's National Inpatient Sample. The study population was 14,312,619 deliveries between 2017 and 2020. Obstetric characteristics and outcomes associated with GC pregnancies were assessed with inverse probability of treatment weighting propensity score.

RESULTS

There were 1965 GCs (13.7 per 100,000) included for national estimates. The prevalence rate of GC pregnancies increased by 55.0% over a 4-year period from 11.8 to 18.2 per 100,000 deliveries (P-trend < .001). In the weighted model, GCs were more likely to have a multiple gestation pregnancy (14.7% vs 1.8%, adjusted odds ratio [aOR] 7.83, 95% confidence interval [CI] 6.54-9.38, P < .001), placental abruption (3.5% vs 1.1%, aOR 2.98, 95%CI 2.12-4.19), and low-lying placenta (1.6% vs 0.2%, aOR 5.14, 95%CI 3.10-8.52). Among singleton delivery, odds of late-preterm (10.8% vs 6.4%, aOR 1.79, 95%CI 1.44-2.23) and periviable (1.1% vs 0.4%, aOR 2.54, 95%CI 1.32-4.89) deliveries and postpartum hemorrhage (12.2% vs 4.1%, aOR 3.27, 95%CI 2.67-4.00) were increased for GC compared to non-GCs whereas odds of cesarean delivery (23.6% vs 31.6%, aOR 0.59, 95%CI 0.51-0.69) were decreased. These associations were less robust in multi-fetal gestations.

CONCLUSION

The results of the current nationwide assessment suggest that GC pregnancies are rare but gradually increasing in the United States. This study shows that GC pregnancies have usually favorable pre-pregnancy patient characteristics compared to non-GC pregnancies, with mixed obstetric outcomes including increased odds of preterm delivery, placental abnormalities, and postpartum hemorrhage and decreased odds of cesarean delivery in singleton pregnancies.

Risks of Placental Abruption and Preterm Delivery in Patients Undergoing Assisted Reproduction

Importance

Patients using assisted reproductive technology (ART) may need additional counseling about the increased risks of placental abruption and preterm delivery. Further investigation into the potential additive risk of ART and placental abruption is needed.

Objective

To ascertain the risk of placental abruption in patients who conceived with ART and to evaluate if placental abruption and ART conception are associated with an increased risk of preterm delivery (<37 weeks' gestation) over and above the risks conferred by each factor alone.

Design, Setting, and Participants

This cross-sectional study used data from the National Inpatient Sample, which includes data from all-payer hospital inpatient discharges from 48 states across the US. Participants included women aged 15 to 54 years who delivered from 2000 through 2019. Data were analyzed from January 17 to April 18, 2024.

Exposures

Pregnancies conceived with ART.

Main Outcomes and Measures

Risks of placental abruption and preterm delivery in ART conception compared with spontaneous conceptions. Associations were expressed as odds ratios (ORs) and 95% CIs derived from weighted logistic regression models before and after adjusting for confounders. The relative excess risk due to interaction (RERI) of the risk of preterm delivery based on ART conception and placental abruption was also assessed.

Results

Of 78 901 058 deliveries, the mean (SD) maternal age was 27.9 (6.0) years, and 9 212 117 patients (11.7%) were Black individuals, 14 878 539 (18.9%) were Hispanic individuals, 34 899 594 (44.2%) were White individuals, and 19 910 807 (25.2%) were individuals of other races and ethnicities. Of the total hospital deliveries, 98.2% were singleton pregnancies, 68.8% were vaginal deliveries, and 52.1% were covered by private insurance. The risks of placental abruption among spontaneous and ART conceptions were 11 and 17 per 1000 hospital discharges, respectively. After adjusting for confounders, the adjusted OR (AOR) of placental abruption was 1.42 (95% CI, 1.34-1.51) in ART pregnancies compared with spontaneous conceptions, with increased odds in White women (AOR, 1.42; 95% CI, 1.31-1.53) compared with Black women (AOR, 1.16; 95% CI, 0.93-1.44). The odds of preterm delivery were significantly higher in pregnancies conceived by ART compared with spontaneous conceptions (AOR, 1.46; 95% CI, 1.42-1.51). The risk of preterm delivery increased when patients had both ART conception and placental abruption (RERI, 2.0; 95% CI, 0.5-3.5).

Conclusions and Relevance

In this cross-sectional study, patients who conceived using ART and developed placental abruption had a greater risk of preterm delivery compared with spontaneous conception without placental abruption. These findings have implications for counseling patients who seek infertility treatment and obstetrical management of ART pregnancies.

The effect of fertility treatment and socioeconomic status on neonatal and post-neonatal mortality in the United States

OBJECTIVE

To determine the association between fertility treatment, socioeconomic status (SES), and neonatal and post-neonatal mortality.

STUDY DESIGN

Retrospective cohort study of all births (19,350,344) and infant deaths from 2014-2018 in the United States. The exposure was mode of conception-spontaneous vs fertility treatment. The outcome was neonatal (<28d), and post-neonatal (28d-1y) mortality. Multivariable logistic models were stratified by SES.

RESULT

The fertility treatment group had statistically significantly higher odds of neonatal mortality (high SES OR 1.59; CI [1.5, 1.68], low SES OR 2.11; CI [1.79, 2.48]) and lower odds of post-neonatal mortality (high SES OR 0.87, CI [0.76, 0.996], low SES OR 0.6, CI [0.38, 0.95]). SES significantly modified the effect of ART/NIFT on neonatal and post-neonatal mortality.

CONCLUSIONS

Fertility treatment is associated with higher neonatal and lower post-neonatal mortality and SES modifies this effect. Socioeconomic policies and support for vulnerable families may help reduce rates of infant mortality.