Study design and study participants

This is a cross-sectional study which was conducted in a tertiary maternity hospital between January 2010 and December 2019. In this study, women who were undergoing ART (including in vitro fertilization (IVF), intracytoplasmic sperm injection (ICSI), frozen-thawing embryo transfer (FET)) and with live birth at the same hospital were enrolled in the study. The study was approved by the Independent Ethics Committee of Guangzhou Women and Children’s Hospital (No. 2022-090A01).

According to the routing protocol, the women were interviewed seven days after delivery by a nurse via telephone. The maternal and neonatal outcomes were recorded based on a self-report from one of the spouses. Meanwhile, the standardized electronic hospitalized discharge records were extracted from the hospital medical database. For each case, maternal and neonatal information obtained from telephone interviews and extracted from medical files were compared.

Data collection via telephone

The couples were informed and signed a follow-up consent form before IVF treatment and were interviewed by telephone seven days after delivery. Data collected via telephone included: date of delivery, mode of delivery, number of children born, gender and birth weight of each baby, congenital malformations of each baby, and maternal/neonatal complications. Data collected via telephone were recorded in the ART database.

To ensure the consistency of the follow-up process, all of the nurses were trained, and a uniform follow-up questionnaire was applied (Additional file 1). If the couples did not answer the first call, additional calls were made three or four days later to maximize the follow-up rate.

When extracting variables from the ART database, personal identification number of the women, IVF/ICSI, fresh/cryopreserved, date of embryo transfer, and number of embryos transferred were extracted for further analysis.

Data collection from standardized electronic hospitalized discharge records

In standardized electronic hospitalized discharge records, all diagnoses of disorders and diseases were coded using the International Statistical Classification of Diseases and Related Health Problems, Eleventh Revision (ICD-11) [19]; all operating procedures were coded by using the ICD-11 and the International Classification of Diseases, 9th Revision. Clinical Modification (ICD-9-CM) [20].

Before the linkage process, a limited data file was generated from standardized electronic hospitalized discharge records, containing only the following factors: women’s personal identification number, woman’s first, middle name or initial, and last names, date of hospitalized discharge, and whole items of discharge diagnosis.

Linkage procedure

We linked the ART database and hospitalized discharge records. In the first step, the women’s personal identification number was cross-linked between the two databases to ensure proper identity recognition. Then the date of hospitalized discharge was linked to the date of embryo transfer to exclude the delivery followed by a spontaneous conception of the same woman. Thirdly, duplicated records were excluded if the women were hospitalized several times during the same conception. Fourthly, the study population was limited to delivery births only; hospitalized discharge without delivery record is also excluded.

Definition of maternal complications neonatal outcomes

Maternal chronic diseases were defined as chronic diseases the pregnant woman had before pregnancy, including thyroid diseases, anemia, and other diseases. Maternal complications were defined as disorders that developed during pregnancy, including pregnancy-induced hypertension (persistent blood pressure ≥ 140/90 mmHg was recorded after 20 weeks of gestation in a previously normotensive woman, preeclampsia and eclampsia), gestational diabetes mellitus, placenta previa, placental abruption, oligohydramnios, polyhydramnios, preterm birth (gestational age at birth, 28–36 weeks), cesarean delivery, abnormal placental cord insertion, postpartum hemorrhage (bleeding volume ≥ 500 mL after vaginal delivery or ≥ 1000 mL after cesarean delivery), and intrahepatic cholestasis of pregnancy. Neonatal outcomes were defined as neonatal complications that developed before or after birth until discharge, including fetal distress, low birth weight (birth weight < 2500 g), macrosomia (birth weight > 4000 g).

Among these variables, low birth weight and macrosomia were identified according to birth weights reported in the records. Preterm birth was accounted for according to birth date and embryo transfer date. Other variables were identified according to the related ICD-9-CM or ICD-10 codes.

Statistical analysis

Categorical variables were expressed as frequency and percentage. Cohen’s kappa (κ) statistics were used to investigate the agreement between records from telephone follow-up and of hospitalized discharge records. Kappa coefficients were interpreted as follows: almost perfect (0.81–1.00), substantial (0.61–0.80), moderate (0.41–0.60), fair (0.21–0.40), and slight (0–0.20) [21, 22]. All data analyses were performed using SPSS for windows 23.0. (IBM, Armonk, NY). P values < 0.05 were considered significant.