Preplanned Studies: Effects of Short Interpregnancy Intervals on Adverse Pregnancy Outcomes — Haidian District, Beijing Municipality, China, 2017–2019

Research has demonstrated that interpregnancy intervals (IPIs) that are notably short or prolonged could escalate the probability of adverse perinatal outcomes (1-2). Particularly, short IPIs (SIPIs) may dramatically amplify the risk of negative pregnancy results (3) and potentially bring about temporary or enduring complications for the fetus (4). This prospective cohort study aimed to examine the pregnancy outcomes amongst various IPI groups of expectant mothers in Beijing’s Haidian District, along with the effects of SIPIs on adverse pregnancy outcomes. These include gestational diabetes mellitus, gestational hypertension, preeclampsia, gestational metabolic syndrome, preterm birth, low birth weight, small size for gestational age, miscarriage, postpartum hemorrhage, fetal distress, and premature membrane rupture. Its ultimate goal was to equip clinicians with empirical data for counseling women on optimal pregnancy spacing. The study is comprised of 1,185 women who had registered a file with Beijing Haidian Maternal and Child Health Hospital and volunteered to contribute to a pregnancy cohort. Our findings revealed that a SIPI was a significant predictor for abortion, postpartum hemorrhage, and fetal distress. It is thus advised to enhance health education among women of childbearing ages, to avert excessively brief IPIs and thereby minimize adverse pregnancy outcomes.

With the inauguration of the universal two-child policy in 2016, followed by the introduction of the three-child policy in 2021, China has witnessed a substantial increase in the number of multiparous women. Consequently, an escalating number of couples are having more than one child, drawing attention to the significance of intervals between pregnancies. Recognized as a potentially modifiable risk factor with implications for perinatal and neonatal outcomes, IPI holds immense importance for both maternal and fetal health. To facilitate superior maternal healthcare and mitigate the incidence of undesirable maternal and fetal outcomes during a subsequent pregnancy, it is imperative to provide appropriate recommendations for the optimal duration of interval before a second pregnancy among women of reproductive age.

This prospective cohort study engaged 3,988 pregnant females at or earlier than 20 weeks of gestation. The engagement took place at Beijing Haidian Maternal and Child Health Hospital between October 2017 and November 2019. After excluding participants with first-time pregnancies, twin or multiple pregnancies, and those lacking information on gravidity or IPI, the final subject group consisted of 1,185 individuals (Supplementary Figure S1). Key demographic characteristics, including maternal age, height, and pre-pregnancy weight, along with pregnancy-related details such as education, occupation, gravidity, parity, accidental pregnancy, contraceptive use, and a history of adverse pregnancy, were gathered through in-person administration of questionnaires. Pregnancy outcomes and associated complications were sourced directly from the hospital case database. All the participants provided consent by signing an informed consent form. The study design was authorized by the pertinent ethics review committee.

In this study, IPI was considered the duration between the conclusion of the preceding delivery — encompassing live births, miscarriages, stillbirths, and abortions — and the start of the subsequent pregnancy. Guidelines from the World Health Organization (WHO) suggest a wait time of at least 24 months from a live birth before embarking on a subsequent pregnancy (5). Adhering to these recommendations, subjects were divided into three categories: very short IPI (VSIPI, <12 months) (6-7), short IPI (SIPI, 12–23.9 months), and normal IPI (NIPI, ≥24 months). The parallel double entry of the survey data was performed using EpiData software (version 3.1, EpiData Association, Odense, Denmark). IBM SPSS (version 26.0; IBM Corp., Armonk, NY, USA) was employed for statistical evaluations. Categorical variables were represented in terms of count (n) and percentage (%). A comparison of the risk for negative pregnancy outcomes among different groups was facilitated through Pearson’s χ² test. Post adjustments for maternal age, education, income, pre-pregnancy body mass index (BMI), adverse maternal history, among other potential confounders, the association between IPI and unfavorable pregnancy outcomes was analyzed via multinomial logistic regression. The results are presented as odds ratios (ORs) alongside 95% confidence intervals (CIs). A P-value less than 0.05 was regarded as indicative of statistical significance.

Table 1 outlines the sociodemographic and maternal attributes of the research subjects. The age range of the participants was from 21–47, with an average age of 35.1±4.1, and they were on average at 11.2±2.2 weeks of gestation when included in the study. Of the 1,185 subjects, 188 (15.9%) had a VSIPI, 217 (18.3%) had a SIPI, while the remaining 780 (65.8%) had an NIPI. The educational background of the participants was predominantly high, with the majority employed as educators, healthcare professionals, or government and corporate workers. Hence, they are broadly representative of high knowledge sectors across the country.

Table 2 illustrates that the prevalence of PTB, LBW, SGA, and PROM in the NIPI group was inferior compared to those in the VSIPI and SIPI groups; however, this discrepancy failed to have statistical significance. In contrast, a significant variation was noted in the incidence of complications such as gestational hypertension, miscarriage, postpartum hemorrhage, and fetal distress across the three subgroups of pregnant women.

Table 3 explicates the impact of VSIPI and SIPI on GHTN, miscarriage, postpartum hemorrhage, and fetal distress. Despite SIPI being identified as a risk factor for miscarriage and fetal distress, the difference lacked statistical significance. A marked rise in the risk for all adverse pregnancy outcomes was observed in the VSIPI group compared to the NIPI group, encompassing miscarriage (OR: 13.388, 95% CI: 4.421–40.537), postpartum hemorrhage (OR: 1.653, 95% CI: 1.077–2.535), and fetal distress (OR: 1.523, 95% CI: 1.031–2.250). However, the odds for gestational hypertension were reduced in the VSIPI group (OR: 0.310, 95% CI: 0.117–0.821) compared to the NIPI group. Thus, it can be concluded that an excessively brief IPI serves as a risk factor for miscarriage, postpartum hemorrhage, and fetal distress.