An interpregnancy interval (IPI) under 18 months or of at least 36 months following healthy live birth increases the risk of subsequent spontaneous abortion (SA), according to a recent study published in JAMA Network Open.1
Takeaways
- Interpregnancy intervals (IPI) of less than 18 months or at least 36 months significantly increase the risk of subsequent spontaneous abortion (SA).
- The safest interpregnancy interval, minimizing the risk of SA, is between 18 to 35 months following a healthy live birth.
- Approximately 23 million miscarriages occur annually worldwide, affecting approximately 15.3% of pregnancies.
- In addition to IPI, other factors contributing to increased SA risk include chromosomal abnormalities, advanced maternal age, passive smoking, air pollution, previous SA, and chronic maternal diseases
- Women with an IPI of under 18 months have a 15% increased risk of SA, while those with an IPI of 36 to 59 months and 60 or more months face a 28% and 113% increased risk, respectively.
Approximately 23 million miscarriages occur annually worldwide, with a pooled risk of 15.3%.2 Of women, 10.8% have experienced 1 miscarriage, 1.9% 2, and 0.7% 3 or more.
SA is associated with multiple adverse obstetrical outcomes, including subsequent SA, placental abruption, and premature birth.1 Additionally, long-term risks such as venous thromboembolism and cardiovascular disease are increased by SA.
Factors increasing SA risk include chromosomal abnormalities, older age, passive smoking, air pollution, previous SA, and chronic maternal diseases. IPI has been proposed as a potential risk factor of SA, but there is little data evaluating this association.1
To evaluate the association between IPI following a healthy live birth and subsequent SA, investigators conducted a national population-based cohort study. Data was obtained from the National Free Prepregnancy Checkups Projects (NFPCP), a program providing free preconception health assessments and follow-up to reproductive-aged couples.
Relevant data at baseline included demographic characteristics, reproductive history, disease history, and lifestyle. Follow-up was performed over telephone by trained local health workers. Participants included women aged 20 to 49 years with 2 instances of NFPCP participation from January 1, 2010, to December 31, 2020.
Pregnancies with a difference between the number of previous pregnancies greater than 1 were excluded from the analysis. Additional exclusion criteria included multiple pregnancies, macrosomia, premature birth, large for gestational age, low birth weight, small for gestational age, stillbirth, and missing information.
IPI was defined as the time between delivery date and the subsequent pregnancy and calculated as the current last menstrual period (LMP) subtracted by the prior delivery date. IPI groups included under 18 months, 18 to 23 months, 24 to 25 months, 36 to 59 months, and 60 months or more.1
SA, determined by fetal death or pregnancy loss, was reported as the primary outcome of the trial based on self-report. Pregnancy outcome data was obtained through telephone follow-up among women with successful conception.
Covariates included maternal age at LMP, prepregnancy body mass index, mode of delivery at prior pregnancy, maternal education level, smoking, alcohol consumption, ethnicity, and abortion history.
There were 180,921 multiparous women included in the final analysis, aged a mean 26.3 years. An IPI under 18 months was reported in 37.4% of individuals, 18 to 23 months in 16.2%, 24 to 35 months in 25.2%, 36 to 59 months in 19.1%, and 60 months or longer in 2.1%.1
There were 4380 SA events reported. SA rates were 2.3% among women with an IPI under 18 months, 2.1% 18 to 23 months, 2.3% 24 to 35 months, 2.8% 36 to 59 months, and 4.9% 60 months or longer. This indicated an odds ratio of 1 for IPIs of 21.7 to 24.6 months.
Compared to patients with in IPI of 18 to 23 months, those with an IPI under 18 months had a 15% increased risk of SA. These increases in risk were 28% among those with an IPI of 36 to 59 months and 113% among those with an IPI of 60 or more months. An IPI of 24 to 35 months was not linked to increased SA risk.
When adopting a reference group of IPI from 18 to 35 months, there was no longer a significant association between an IPI under 18 months and SA.These trends were similar in sensitivity analyses and subgroup analyses based on mode of delivery.
These results indicated an increased risk of SA following an IPI of under 18 months or of 36 months or longer. Investigators concluded these results may facilitate SA prevention and improvement in neonatal outcomes.1
References
- Hu X, Yang Y, Wang L, et al. Interpregnancy interval after healthy live birth and subsequent spontaneous abortion. JAMA Netw Open. 2024;7(6):e2417397. doi:10.1001/jamanetworkopen.2024.17397
- Siobhan Quenby P, Gallos ID, Dhillon-Smith RK, et al. Miscarriage matters: the epidemiological, physical, psychological, and economic costs of early pregnancy loss. Lancet. 2021;397(10285):1658-1667. doi:10.1016/S0140-6736(21)00682-6
