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Multicenter Study
. 2025 Aug 30;25(1):2983.
doi: 10.1186/s12889-025-24466-6.

The optimal childbearing age and birth spacing in china: a multicenter retrospective cohort study

Zhijia Zhao  1   2 , Hui Zhu  3 , Hongyi Liu  2 , Yanming Chen  2 , Qiong Zhu  4 , Jie Cai  5 , Jin Xu  6 , Qinkang Lu  7 , Lindan Ji  8   9
Affiliations
Multicenter Study

The optimal childbearing age and birth spacing in china: a multicenter retrospective cohort study

Zhijia Zhao et al. BMC Public Health. .

Abstract

Background: We aimed to comprehensively analyze the impact of both maternal age and birth spacing on adverse maternal and neonatal outcomes.

Methods: A total of 151,301 pregnancies in China from January 1, 2010, to December 31, 2021 were included, and 8,222 subjects matched their primary and second pregnancy information. Join point regression was used to analyze the temporal trends of adverse outcomes with maternal age and birth spacing.

Results: The mean maternal age at delivery rose from 27.1 years to 28.5 between 2010 and 2021, and the average annual percentage change in advanced maternal age (≥ 35 years) was 1.2%. The optimal childbearing age (with the fewest adverse outcomes) appears to be 27 years. Compared with women aged 27 years, both those aged < 27 years and those aged > 27 years exhibited a significantly higher risk of anemia, low birth weight (LBW), preeclampsia, and preterm birth. In addition, we found that the optimal primiparous childbearing age was 26 years old and birth spacing was 3 years, < 3 years increased the risk of FGR, oligohydramnios, placenta previa, preeclampsia, LBW, preterm birth and premature rupture of membranes (PROM). While birth spacing > 3 years significantly increased the risks of anemia, gestational diabetes mellitus (GDM), placenta previa, preeclampsia, thyroid dysfunction (TD), preterm birth and PROM. The subgroup analysis revealed that the common adverse outcomes increased with longer birth spacing in pregnant women < 26 years, while these adverse outcomes showed lowest prevalence rates at 3-year birth spacing in pregnant women > 26 years.

Conclusions: The age of childbearing continues to be delayed, and we are in favor of having children at relatively optimal ages and spacing.

Keywords: Adverse outcomes; Birth spacing; Joinpoint regression analysis; Maternal age.

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Conflict of interest statement

Declarations. Ethics approval and consent to participate: The study was carried out in accordance with guidelines of the Declaration of Helsinki. The study was approved by the Research Ethics Committees of Ningbo University Medical Science, Affiliated People’s Hospital of Ningbo University, Ningbo Women & Children’s Hospital, and Beilun People’s Hospital of Ningbo. We used secondary medical data provided by hospitals, and all sensitive information (such as name, identification card number, medical insurance account, address, telephone number, work unit, etc.) were removed prior to data analysis according to the information security technology guide for health data security of China. The Research Ethics Committees of Ningbo University Medical Science, Affiliated People’s Hospital of Ningbo University, Ningbo Women & Children’s Hospital, and Beilun People’s Hospital of Ningbo did not require the use of informed consents. Consent for publication: Not applicable. Competing interests: The authors declare no competing interests.

Figures

Fig. 1
Fig. 1
Flow chart of the study participants
Fig. 2
Fig. 2
The trend of adverse outcomes incidence in relation to maternal age
Fig. 3
Fig. 3
Logistic regression analysis of the association between age and adverse outcomes
Fig. 4
Fig. 4
Nomogram to predict the risk of adverse outcomes in next pregnancy
Fig. 5
Fig. 5
The trend of incidence for pregnancy complications at various birth spacing
Fig. 6
Fig. 6
Logistic regression analysis of the association between birth spacing and adverse outcomes
See this image and copyright information in PMC

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