What causes fgr in pregnancy

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Last updated: April 4, 2026

Quick Answer: Fetal growth restriction (FGR) in pregnancy, formerly known as intrauterine growth retardation, occurs when a fetus doesn't grow at the expected rate within the womb. This can be due to issues with the placenta, maternal health conditions, or genetic factors affecting the baby.

Key Facts

FGR affects approximately 3-10% of pregnancies.
The most common cause of FGR is placental insufficiency.
Conditions like preeclampsia, hypertension, and diabetes in the mother increase FGR risk.
Smoking during pregnancy is a significant modifiable risk factor for FGR.
Early detection and management can improve outcomes for babies with FGR.

Overview

Fetal Growth Restriction (FGR), previously referred to as intrauterine growth retardation (IUGR), is a condition where a baby in the womb does not grow as expected. It is diagnosed when a baby's estimated weight is below the 10th percentile for gestational age. This means that out of 100 babies of the same gestational age, at least 90 would be expected to weigh more than the baby diagnosed with FGR. FGR is a serious concern because babies who are too small are at increased risk for complications during pregnancy, labor, and the newborn period. These complications can include stillbirth, birth asphyxia, and long-term developmental issues.

Causes of Fetal Growth Restriction

The causes of FGR are diverse and can be broadly categorized into three main groups: factors related to the fetus, factors related to the placenta, and factors related to the mother.

Fetal Factors

In some cases, the fetus itself may have a genetic abnormality or a chromosomal condition that limits its growth potential. Conditions such as Down syndrome, Trisomy 18, and other genetic disorders can lead to a smaller than average baby. Certain congenital infections acquired during pregnancy, like cytomegalovirus (CMV), rubella, or toxoplasmosis, can also impair fetal development and result in FGR.

Placental Factors

The placenta plays a crucial role in providing the fetus with oxygen and nutrients from the mother. Problems with the placenta are the most common cause of FGR. This can include:

Placental Insufficiency: The placenta may not develop properly or may not be able to deliver enough blood, oxygen, and nutrients to the baby. This can be due to issues with the blood vessels in the placenta or a small placental size.
Placental Abruption: Although less common as a primary cause of chronic FGR, partial abruption (where the placenta partially detaches from the uterine wall) can compromise blood flow.
Umbilical Cord Abnormalities: Issues with the umbilical cord, such as a single umbilical artery instead of two, or a cord that is too short or too long, can affect nutrient and oxygen delivery.

Maternal Factors

The health and lifestyle of the mother significantly impact fetal growth. Several maternal conditions and behaviors are associated with an increased risk of FGR:

Maternal Health Conditions:
- Hypertension (High Blood Pressure): Chronic hypertension or gestational hypertension (including preeclampsia) can reduce blood flow to the placenta.
- Diabetes Mellitus: Poorly controlled diabetes can paradoxically lead to both macrosomia (large baby) and FGR, depending on the stage and control of the condition.
- Heart, Lung, and Kidney Disease: Chronic conditions affecting major organ systems can impact the mother's ability to support fetal growth.
- Infections: Certain maternal infections can cross the placenta and affect the fetus.
- Anemia: Severe maternal anemia can limit oxygen supply to the fetus.
Maternal Lifestyle and Environment:
- Smoking: Nicotine constricts blood vessels, reducing blood flow to the placenta and is a major preventable cause of FGR.
- Alcohol and Drug Use: Recreational drug use and heavy alcohol consumption can interfere with fetal development.
- Malnutrition: Inadequate nutritional intake by the mother limits the building blocks necessary for fetal growth.
- Advanced Maternal Age: Women over 35 may have a slightly higher risk.
- Previous FGR: A history of FGR in a prior pregnancy increases the risk in subsequent pregnancies.
- Multiple Gestations: Carrying twins, triplets, or more babies can sometimes lead to restricted growth due to competition for resources.

Diagnosis and Management

FGR is typically suspected when a pregnant woman's fundal height (the distance from the pubic bone to the top of the uterus) is smaller than expected for her gestational age. This suspicion is usually confirmed with ultrasound scans, which measure the baby's size, amniotic fluid volume, and blood flow through the umbilical cord and to the baby's brain. Doppler ultrasound is particularly important for assessing placental function and fetal well-being.

Management of FGR focuses on monitoring the baby's growth and well-being closely and determining the safest time and mode of delivery. If FGR is diagnosed, frequent ultrasounds and fetal monitoring tests (like non-stress tests or biophysical profiles) are usually recommended. The goal is to optimize the pregnancy for as long as safely possible while preparing for the birth of a potentially vulnerable baby. Delivery may be recommended earlier than the due date if the baby's condition deteriorates or if the pregnancy poses a greater risk than delivery.

Importance of Prenatal Care

Regular prenatal visits are crucial for identifying risk factors and monitoring fetal development. If you have concerns about your baby's growth or any of the risk factors mentioned, discuss them openly with your healthcare provider. Early detection and appropriate management are key to improving outcomes for both mother and baby in cases of FGR.