Multicenter Prospective Cohort Study of Twin Maternal-Child Dyads in China

Rate of preterm delivery

Preterm delivery is defined as delivery between 28 and 37 gestational weeks.

Rate of preeclampsia

Preeclampsia is defined as the condition occurring in pregnant women after 20 weeks of gestation, characterized by systolic blood pressure ≥140 mmHg and/or diastolic blood pressure ≥90 mmHg, accompanied by any of the following: a urinary protein quantification ≥0.3 g/24 h, or a urine protein/creatinine ratio ≥0.3, or random urine protein ≥ (+) (as a method of examination when protein quantification is not feasible). In the absence of proteinuria, the condition may still be diagnosed if there is involvement of any organ or system, including but not limited to critical organs such as the heart, lungs, liver, kidneys, or abnormalities in the hematological, digestive, or neurological systems, as well as complications affecting the placenta-fetus.

Rate of twin-to-twin transfusion syndrome (TTTS)

TTTS is diagnosed in monochorionic diamniotic twin pregnancies when there is a discordance in amniotic fluid volumes, with one fetus exhibiting polyhydramnios and the other oligohydramnios. Specifically, before 20 weeks of gestation, the condition is diagnosed if one fetus (the recipient) has a deepest vertical pocket (DVP) of amniotic fluid ≥8cm, while the other fetus (the donor) has a DVP ≤2cm; after 20 weeks of gestation, the diagnosis is made if one fetus (the recipient) has a DVP ≥10cm, while the other fetus (the donor) has a DVP ≤2cm.

Rate of selective fetal growth restriction (sFGR)

sFGR is diagnosed in monochorionic diamniotic twin pregnancies when one fetus has an estimated fetal weight below the 10th percentile for its gestational age, and there is a discrepancy of ≥25% in the estimated fetal weights between the two fetuses.

Rate of sleep disorders

Women's physiological and psychological changes during pregnancy will affect sleep, and the occurrence of bad sleep during pregnancy is more common. It is generally assessed by a sleep questionnaire.

Rate of mental and phycological disorders

Maternal mental health is as important as physical health, and good maternal mental health helps to promote the physical and mental health of the baby, as well as their own physical condition and natural childbirth. The condition of pregnant women is generally assessed by psychiatric departments.

Rate of single intrauterine fetal demise

The death of one fetus for twin pregnancy，the occurrence in the second and third trimesters of pregnancy has substantial adverse effects on surviving infants.

Rate of gestational hypertension

Take two consecutive measurements on the same arm, the systolic blood pressure more than 140 mmHg and (or) the diastolic blood pressure more than 90 mmHg. High blood pressure may lead to severe complications such as preclampsia and clampsia.