When a fetus is measured via ultrasound and discovered to be below the 10th percentile of weight for its age, fetal growth restriction is typically diagnosed. Also called intrauterine growth restriction (IUGR), this condition is caused by a lack of nutrients or oxygen to the fetus stemming from a variety of factors.
Placental Abnomalities
Problems with the placenta are the most common cause of fetal growth restriction. The placenta is the tissue that attaches to the uterine wall and transfers nutrient-rich blood from the mother through the umbilical cord to the fetus. Placenta previa, a condition in which the placenta attaches to the uterine wall close to the cervix, and placental abruption, the detachment of the placenta from the uterine wall, can both contribute to intrauterine growth restriction. A malformed placenta may also be a potential cause of fetal growth restriction.
Pregnancy Induced Hypertension
Pregnancy-induced hypertension, also known as preeclampsia, is a condition in which the mother's blood pressure rises after the 20th week of pregnancy. Hypertension caused by pregnancy limits the amount of blood flow to the uterus, which may subsequently slow fetal growth. Only some mothers with preeclampsia will have growth-restricted babies, but there is no way yet to determine which individuals will develop IUGR. There does seem to be a correlation, however, between IUGR and the onset of pregnancy-induced hypertension early in the pregnancy.
Birth Defects
Birth defects may result in smaller than normal babies as a result of the defect itself or due to an inability on the part of the fetus to properly process nutrients from the mother. Down syndrome, other chromosomal defects, anencephaly, kidney abnormalities and problems with the abdominal wall have all been implicated as potential contributors to fetal growth restriction.
Umbilical Cord Problems
Velamentous insertion of the umbilical cord, in which the umbilical cord inserts into or close to the membranes, can slow fetal growth. Other umbilical cord problems that may hamper fetal growth include structural problems with the cord itself, such as having a single umbilical artery instead of the normal two, having a knot in the cord or the wrapping of the cord around the body of the fetus.
Mother's Lifestyle
Because the fetus is dependent on his mother for all of his nutrition and blood supply, everything the mother puts into her body can have an effect on the baby. Lifestyle factors that affect an unborn baby's growth include poor nutrition, smoking, drinking alcohol and using certain illegal or prescription drugs.
Maternal Health
Many different types of diseases in the mother can affect an unborn baby's growth. If the pregnant woman has diseases like sickle cell anemia, chronic high blood pressure, heart disease, diabetes or kidney disease, the unborn infant may be smaller than normal. Infection with rubella, cytomegalovirus (CMV), toxoplasmosis, hepatitis B, HIV or syphilis in a pregnant woman can also stifle the growth of the fetus.
