Delayed development of the first baby in the womb is not always the case when the second baby is conceived, depending on the development of the embryo and the condition of the pregnant woman herself.
Factors affecting fetal growth include maternal nutritional supply, placental transfer and fetal genetic potential, and the etiology is complex.
Maternal factors include nutritional factors, pregnancy complications and comorbidities such as hypertensive disorders of pregnancy, maternal age, weight, economic status, smoking, drug use, and so on.
Fetal factors include decreased growth hormone, insulin-like growth factor, leptin and other substances that regulate fetal growth in the umbilical cord blood, which may affect fetal endocrinology and metabolism; fetal genetic or chromosomal abnormalities, structural abnormalities, and so on.
Placental factors include sail-like placenta, contoured placenta, parafollicular placenta, small placenta, and other various lesions of the placenta that lead to reduced uteroplacental blood flow and insufficient blood supply to the fetus.
Umbilical cord factors include single umbilical artery, excessively long umbilical cord, excessively thin umbilical cord, twisted umbilical cord, and knotted umbilical cord.
If the above factors are present during pregnancy, developmental delay may occur. If the above factors are not present during pregnancy, it is generally more likely that the fetus will develop normally.