A baby cannot “starve” in the traditional sense while in the womb because the body has evolved powerful mechanisms to protect the fetus. The concern is not about the baby running out of food, but about a medical condition called Fetal Growth Restriction (FGR). This condition happens when the fetus is unable to reach its full growth potential due to impaired delivery of nutrients and oxygen, which is often a problem with the placenta. Doctors monitor this clinical reality of impaired growth closely.
How the Fetus Receives Nutrition
The placenta is the temporary organ that functions as the life support system for the developing fetus. This structure is an interface between the maternal and fetal blood supplies, which do not directly mix. The placenta is fully formed by 18 to 20 weeks of gestation, but it begins its function much earlier, taking over nutrient supply at about 8 to 12 weeks. It acts as a delivery system, transporting essential substances like glucose, oxygen, amino acids, and water from the mother’s bloodstream to the baby’s circulation via the umbilical cord. This system demonstrates a “fetal priority,” meaning the placenta actively works to shuttle nutrients to the fetus, sometimes at the expense of the mother’s reserves. The placenta also manages waste, transferring carbon dioxide and metabolic byproducts from the fetal circulation back into the mother’s blood for elimination.
Understanding Fetal Growth Restriction
Fetal Growth Restriction (FGR), also known as Intrauterine Growth Restriction (IUGR), is the clinical diagnosis for a baby not getting enough nourishment. It is defined as a failure of the fetus to achieve its genetically determined growth potential, typically estimated by a fetal weight below the 10th percentile for its gestational age. FGR is a pathological process caused by a problem in the pregnancy, distinguishing it from a fetus that is simply Small for Gestational Age (SGA). A baby is considered SGA if their size is below the 10th percentile, but they are growing at a normal rate and are not experiencing a pathological restriction. FGR is categorized into two main types based on when the growth impairment begins.
Symmetrical FGR
Symmetrical FGR involves a proportional reduction in the size of all fetal organs, suggesting the restriction began early in pregnancy.
Asymmetrical FGR
Asymmetrical FGR is more common, occurring later in the pregnancy, and is characterized by the fetus prioritizing blood flow to the brain (“brain-sparing”). In asymmetrical FGR, the head and brain may be normal-sized, but the abdomen is smaller.
Why Growth Restriction Occurs
The primary underlying reason for FGR is a failure of the nutrient delivery system, most commonly due to placental insufficiency. This condition occurs when the placenta does not develop correctly or its function declines prematurely, leading to an inadequate supply of oxygen and nutrients to the fetus. The issue often stems from a failure of the maternal blood vessels to properly adapt to the demands of pregnancy, resulting in diminished blood flow to the placenta. Other causes are categorized into maternal, fetal, and placental factors.
- Maternal conditions include chronic high blood pressure, preeclampsia, kidney disease, autoimmune disorders, smoking, alcohol consumption, and severe malnutrition.
- Fetal factors include chromosomal abnormalities, congenital infections, or multiple gestation pregnancy.
Detection and Medical Intervention
Medical professionals monitor for potential growth issues using a combination of routine and specialized assessments. Routine prenatal visits include measuring fundal height. If this measurement is significantly smaller than expected for the gestational age, it can raise the suspicion of FGR. If FGR is suspected, a diagnostic ultrasound is performed to estimate the fetal weight and measure specific body parts like the head circumference and abdominal circumference. An additional tool is the Doppler flow study, which assesses blood flow in the umbilical artery and other fetal vessels. Abnormal Doppler findings indicate impaired placental function and help differentiate true FGR from a constitutionally small fetus. Management strategies for diagnosed FGR focus on careful fetal surveillance, including frequent monitoring with non-stress tests and biophysical profiles. The only definitive treatment for a failing placenta is delivery, and the timing is determined by balancing the risks of prematurity against the dangers of continued growth restriction in utero.