A fetus in utero develops on a specific timetable, with the third trimester devoted mostly to gaining weight. (see reference 3 intro)In 3 to 10 percent of pregnancies, according to the University of California San Francisco, fetal growth lags in the last few months of pregnancy, a condition known as intrauterine growth retardation or restriction, often shortened to IUGR. IUGR increases the risk of dying before or around the time of birth four to eightfold, and 50 percent of those who survive have some health problems. (see reference 1). Maternal, fetal and placental factors all cause IUGR.
Maternal Factors
The main maternal cause of IUGR is high blood pressure, which causing around one third of all cases of IUGR, the United Nations University states. (reference 3, maternal disorders). Other maternal factors associated with IUGR include kidney disease, with around 9 percent of babies born to mothers with kidney disease having IUGR, diabetes, lung or heart disease. Cigarette smoking during pregnancy after 16 weeks also increases the risk of IUGR, (reference 3)and the risk increases the more a mother smokes. Alcohol use in much lower amounts than associated with fetal alcohol syndrome and opiate use in pregnancy also can cause IUGR. Poor diet, low maternal weight and poor weight gain also are implicated in IUGR, along with young maternal age, poverty, recent pregnancy and high number of previous births.
Placental Factors
The placenta supplies nutrients to the fetus and removes waste products, so diseases that interfere with its functioning, such as high blood pressure, diabetes and kidney disease can cause IUGR. Other causes of decreased blood flow include a placenta that implants too low on the uterine wall, called placenta previa, placental abruption, where part or all of the placenta detaches prematurely from the uterine wall and infection, according to the Lucile Packard Children's Hospital at Stanford. Uterine malformations can also affect placental implantation and lead to IUGR. (see reference 1)
Fetal Factors
Genetic anomalies and chromosomal defects can cause IUGR in a fetus. Fetal exposure to TORCH infections, which include toxoplasmosis, rubella, cytomegalovirus and herpes simplex or varicella, the virus that causes chicken pox, can lead to IUGR. Prenatal infections often have a poor long term prognosis, the University of California San Francisco warns. Multiple pregnancies also increase the risk of IUGR; identical twins who share a placenta develop twin to twin transfusion syndrome, where one twin receives too much of the blood supply and one receives too little, developing IUGR. Twin to twin transfusion syndrome affects 10 to 15 percent of such pregnancies, the University of California San Diego notes.
References
- University of California San Francisco: Intrauterine Growth Retardation
- Lucile Packard Children's Hospital at Stanford: Intrauterine Growth Restriction
- United Nations University: Causes and Consequences of Intrauterine Growth Retardation
- Children's Hospital Boston: Other In Utero TORCH Infections
- University of California San Diego:Twin to Twin Transfusion Syndrome
