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

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

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.

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.

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.

Fetal brain injury is an abnormality in the structural and functional integrity of the cerebrum, cerebellum, or brainstem during the gestational period, caused by various factors such as hypoxic-ischemic events, infections, hemorrhage, congenital malformations, and genetic metabolic disorders.

Brain injury refers to damage to the central nervous system resulting from various risk factors during pregnancy, childbirth, and the neonatal period. Clinically, it manifests as central motor disorders, cognitive impairments, language disorders, visual and auditory impairments, as well as difficulties in social interaction and psychological and behavioral disorders. It needs pregnant history or birth history, (such as one of twin intrauterine fetal death, Intrauterine distress), manifestation, and ultrasound, CT, MRI, electroencephalogram to make a definite diagnosis.

Early childhood developmental delay of the offspring refers to a significant lag or delay in achieving age-appropriate developmental milestones across one or more domains, including cognitive, language, motor, social-emotional, and adaptive skills, during the early years of life (typically from birth to 5 years of age) in comparison to established norms or peers. The assessment of early childhood developmental delay is conducted using standardized scales such as Ages Stages Questionnaires (Third Edition), Gesell Developmental Schedules, and Bayley Scales of Infant and Toddler Development. The actual measurement process will be depending on the routine pediatric settings and resources available at each participating institution.

Each child is measured twice. If the difference is less than 0.1 cm, the average of the two measurements is taken. If the difference is greater than 0.1 cm, the measurement is repeated.

Each newborn is measured twice. If the difference is less than 0.01 kg, the average of the two measurements is taken. If the difference is greater than 0.01 kg, the measurement is repeated.

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.

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.

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.

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.

Diagnosed with gestational diabetes through an oral glucose tolerance test (OGTT). The blood glucose threshold of fasting, 1 h and 2 h after taking oral glucose was 5.1, 10.0, 8.5 mmolL, respectively, and the blood glucose level reached or exceeded the above criteria at any time point was diagnosed as GDM. GDM is clearly associated with adverse pregnancy outcomes such as fetal macrosomia, cesarean section delivery, preterm birth, and preeclampsia

Deaths during pregnancy or less than 42 days after termination of pregnancy.

After 28 gestational weeks, the fetus dies before or during delivery

Each newborn is measured twice. If the difference is less than 0.01 kg, the average of the two measurements is taken. If the difference is greater than 0.01 kg, the measurement is repeated.

Each newborn is measured twice. If the difference is less than 0.1 cm, the average of the two measurements is taken. If the difference is greater than 0.1 cm, the measurement is repeated.