Fetal Growth Restriction: Causes, Signs, and Risks for Pregnancy

What is fetal growth restriction and why does it occur?

Fetal growth restriction (FGR), or fetal retardation, is a condition in which a fetus fails to reach its potential size and weight for a given gestational age. This can be caused by a multitude of factors affecting its growth and development in the womb. FGR is a serious pregnancy complication that can lead to an increased risk of neonatal morbidity and mortality, as well as long-term health problems for the child. Understanding the causes and timely diagnosis play a key role in managing this condition.

Maternal risk factors: when maternal health affects the fetus

Maternal health before and during pregnancy has a direct impact on fetal development. A number of chronic diseases and conditions can significantly increase the risk of FGR:

• Budd-Chiari syndrome: This is a rare disease characterized by hepatic venous outflow obstruction, often associated with hypercoagulable states. Pregnancy itself is a prothrombotic state that can trigger the onset of the disease. In one case, despite the stabilization of the mother's condition and normal fetal growth, the pregnancy ended in intrauterine fetal demise at 34 weeks due to placental abruption [1].
• Atrial fibrillation: The development of new-onset atrial fibrillation (AF) during pregnancy is rare, but its occurrence can cause hemodynamic changes that negatively affect both the mother and the fetus, potentially leading to adverse outcomes [5].
• Juvenile hemochromatosis: This is a rare iron metabolism disorder leading to iron overload and organ failure. Delayed diagnosis can lead to severe complications, including endocrine disorders and heart failure, which indirectly affects reproductive health and pregnancy [7].
• Subclinical hypothyroidism (SCH): Studies show an association between methylenetetrahydrofolate reductase (MTHFR) gene polymorphisms and SCH in early pregnancy. SCH, in turn, is associated with an abnormal pre-pregnancy body mass index (BMI) and a history of anemia [8], which can affect fetal development.
• Epilepsy and anticonvulsant use: Women with epilepsy undergoing fertility treatment often take various anticonvulsant medications and hormone therapies [6]. While the direct impact on FGR is not always obvious, maternal disease control and medication management require careful monitoring.

Metabolic and endocrine disorders

Obesity and polycystic ovary syndrome (PCOS) are significant factors affecting reproductive health and the course of pregnancy:

• PCOS and obesity: In PCOS patients undergoing IVF, obesity is associated with a thinner endometrium, reduced endometrial blood flow, and a higher uterine artery resistance index. These factors can negatively affect embryo implantation [4], and consequently, subsequent fetal development.
• Abnormal pre-pregnancy BMI: As mentioned earlier, an abnormal pre-conception BMI is a risk factor for the development of subclinical hypothyroidism in early pregnancy [8], which can indirectly affect fetal growth.

Placental and uterine causes

The placenta plays a critical role in supplying the fetus with oxygen and nutrients. Any impairment in its function or structure can lead to FGR:

• Placental abruption: This is an obstetric emergency in which the placenta separates from the uterine wall before the baby's birth. Abruption can be traumatic or spontaneous and leads to a sharp disruption of fetal blood supply, which can cause intrauterine death [1, 3].
• Fetomaternal hemorrhage: A condition in which fetal blood enters the maternal circulation, also an obstetric emergency [3].
• Uterine blood flow abnormalities and endometrial condition: Insufficient uterine blood supply and a thin endometrium, especially in women with PCOS and obesity, can impede normal implantation and placental development, ultimately affecting fetal growth [4].

Signs and diagnosis of fetal growth restriction

Early detection of FGR is crucial for improving pregnancy outcomes. Main signs and diagnostic methods include:

• Smaller uterine size: During regular check-ups, the doctor measures the fundal height. If this indicator significantly lags behind the norm for the gestational age, it may indicate FGR.
• Ultrasound examination (US): This is the main diagnostic method for FGR. Ultrasound is used to evaluate fetal biometric parameters (head and abdominal sizes, femur length), which are compared with standard values. Doppler ultrasound assesses blood flow in the placental and fetal vessels (e.g., umbilical artery, middle cerebral artery), identifying signs of placental insufficiency.
• Fetal movement monitoring: Decreased fetal activity can be a warning sign.

It is important to note that certain conditions, such as migraine with aura triggered by hormonal fluctuations during IVF, may manifest as maternal brain lesions [2]. While not directly related to FGR, any severe deterioration in maternal health requires attention and can indirectly affect the pregnancy.

Prevention and management

Pregnancy management in cases of risk or diagnosed FGR requires a comprehensive approach:

• Preconception care: Optimizing health status before conception, controlling chronic conditions (e.g., thyroid disorders, diabetes mellitus, blood pressure).
• Regular monitoring: Frequent doctor visits, regular ultrasounds, and Doppler studies to monitor fetal growth and well-being.
• Multidisciplinary approach: In complex cases, such as Budd-Chiari syndrome, the involvement of a team of specialists, including hepatologists, hematologists, obstetricians, and neonatologists, is required [1].
• Lifestyle modification: Maintaining a healthy BMI before and during pregnancy, a balanced diet, and quitting bad habits.

Timely detection and adequate management of FGR significantly improve the chances of giving birth to a healthy child and minimize risks for the mother.

Sources

1. Budd-Chiari Syndrome Manifesting in Pregnancy: Case Report and Review of Management and Outcomes. https://pubmed.ncbi.nlm.nih.gov/42647303/
2. Cytotoxic Lesion of the Corpus Callosum Related to Migraine With Aura Triggered by In Vitro Fertilization and Embryo Transfer: A Case Report. https://pubmed.ncbi.nlm.nih.gov/40677431/
3. Obstetric and gynecologic emergencies. https://pubmed.ncbi.nlm.nih.gov/9183280/
4. The clinical value of ultrasound parameters combined with clinical indicators in predicting embryo implantation rates in polycystic ovary syndrome patients at different body mass index levels. https://pubmed.ncbi.nlm.nih.gov/42643302/
5. Management of Ablation-Refractory Atrial Fibrillation During Pregnancy. https://pubmed.ncbi.nlm.nih.gov/41503278/
6. Infertility treatment in women with epilepsy: A systematic review. https://pubmed.ncbi.nlm.nih.gov/42492305/
7. Delayed diagnosis of juvenile hemochromatosis due to missed ferritin testing in a case of hypogonadotropic hypogonadism. https://pubmed.ncbi.nlm.nih.gov/42273281/
8. Association Between MTHFR Gene Polymorphisms and Subclinical Hypothyroidism in Early Pregnancy: A Retrospective Case-Control Study. https://pubmed.ncbi.nlm.nih.gov/42338702/

Disclaimer: The information provided in this article is for reference purposes only and cannot replace professional medical advice, diagnosis, or treatment. Always consult a qualified physician regarding any questions concerning your health or the health of your child.