This is a randomized controlled trial, aiming to evaluate the effects of time window for umbilical cord clamping during cesarean section on the health outcomes of offspring hemoglobin，maternal blood loss，and children's growth and development. It will be conducted in Liuyang city and Huantai county of China, and the targeted sample size is 360 (180 in each site). All the eligible pregnant women will be randomly assigned to one of the four groups (three intervention groups and one control group), and their babies will be followed up to 18 months of age.

The World Health Organization and American College of Obstetricians and Gynecologists have recommended a delay in umbilical cord clamping after birth, irrespective of delivery modes, which was based on studies from vaginal deliveries rather than cesareans. In cesareans, the optimal time window for umbilical cord clamping has not been determined, and the relevant safety data are limited. In this randomized study, the investigators aim to evaluate the impacts of time window for umbilical cord clamping during cesarean section on maternal and child health outcomes, and to evaluate the optimal timing of the clamping. The investigators are planning to enroll 360 pregnant women scheduled for cesareans, and to randomly allocate them into four groups: the umbilical cord will be clamped within 15 seconds (immediately), or delayed after deliveries for 30, 60, and 90 seconds, respectively. Babies will be followed up at 3, 6, 12, and 18 months of age. Maternal hemoglobin before and after cesareans, neonatal hemoglobin, children's hemoglobin at 6, 12, 18 months of age will be measured. At each follow-up visit, children's length and weight will be measured, their development will be assessed, and a questionnaire survey including information on feeding, sleep, and medication will be conducted. The primary outcomes are the neonatal hemoglobin and the change in maternal hemoglobin. The secondary outcomes include the incidence rate of neonatal anemia and jaundice, Apgar score, the incidence rate of neonatal intensive care unit (NICU) admission, placental weight, maternal hemoglobin after the cesarean, estimated maternal blood loss, and the incidence rate of maternal blood transfusion. In addition, the children's hemoglobin, anemia, growth and development are considered as the exploratory secondary outcomes.

Inclusion Criteria:

• local resident in Liuyang city, Huantai county and their surrounding areas
• Singleton pregnancy
• Elective caesarean, or cesarean section after the start of labor but the cervix is less than 3 cm
• Term pregnancy (≥37 weeks of gestation), and the fetal weight was estimated ≥2500g by intrauterine ultrasound
• Written informed consent is obtained

Exclusion Criteria:

• Pregnant women with the following risk factors: severe hypertension (systolic blood pressure ≥160 mmHg and/or diastolic blood pressure ≥110mmHg), preeclampsia, chronic hypertension with preeclampsia, diabetes mellitus with severe microangiopathy, placenta previa, placenta implantation, placental abruption, intrauterine distress, prenatal infection, severe anemia (hemoglobin<7g/dL), coagulation disorders, thrombosis disease
• Plan to retain cord blood
• Rh-negative pregnant women
• Prenatal diagnosis of fetal abnormalities which may lead to difficulties in cesareans or adverse pregnancy outcomes, such as abnormal heart monitoring, fetal distress, malformation, anemia, and intrauterine growth restrictions
• Other conditions not suitable for intervention as judged by obstetricians

The IPD will be shared upon the request of other researchers, and all the key variables that will be reported in the main paper are planned to be shared

After the publication of the main paper (hopefully before the end of 2024), the data will be available to share to other researchers

Researchers should request the data via the following Email: lihongtian@pku.edu.cn or liujm@pku.edu.cn