Can fetal “ultrasound major malformation screening” screen and diagnose “patent foramen ovale”?

Author: Zhao Fangui, Chief Physician, Obstetrics and Gynecology Hospital, Fudan University

Reviewer: Kong Fanbin, Chief Physician, Obstetrics and Gynecology Hospital, Fudan University

Figure 1 Copyright image, no permission to reprint

In fact, in addition to the foramen ovale, the other three life channels of the fetus are also open during the fetal period: the ductus arteriosus, the ductus venosus, and the umbilical blood vessels (including two umbilical arteries and one umbilical vein). Today we will focus on the foramen ovale.

1. Fetal period

The foramen ovale is located in the middle and lower part of the atrial septum of the heart and is a physiological channel during the embryonic period. Highly oxygenated blood from the umbilical vein enters the right atrium directly through the inferior vena cava through the ductus venosus, and then enters the left atrium through the foramen ovale to supply the fetus's head, neck, upper limbs and heart. There is an oval valve on the foramen ovale that opens to the left atrium, so that blood does not flow back into the right atrium. Therefore, during the mid-pregnancy ultrasound screening for major malformations (commonly known as "major malformation screening"), the fetal foramen ovale itself is open, so "patent foramen ovale" cannot be diagnosed. If the foramen ovale is closed during the fetal period, it will cause fetal hemodynamic abnormalities.

Figure 2 Copyright image, no permission to reprint

2. Neonates and infants

After birth, the pressure in the newborn's left atrium increases, causing the foramen ovale flap that opens to the left atrium to cling to the edge of the foramen ovale, resulting in functional closure, which is generally achieved anatomically 5 to 7 months after birth. If a newborn is found to have a patent foramen ovale during congenital heart disease screening, don't worry too much. You can follow up with a pediatric cardiac ultrasound examination six months or one year after birth, and the foramen ovale may close naturally by then.

3. Early childhood and beyond

After the anatomical closure of the foramen ovale, an oval shallow depression called the "oval fossa" will form on the atrial septum. If the child is older than 3 years old and the foramen ovale is still not closed, it is diagnosed as "patent foramen ovale". Because the pressure difference between the left and right atria is small, the shunt volume is small, and there is no obvious effect on the hemodynamics of the heart, therefore, it was previously believed that patent foramen ovale had no clinical significance. However, clinical studies in recent years have found that patent foramen ovale is related to migraine, stroke, and hypoxemia. Therefore, once diagnosed with "patent foramen ovale", regular follow-up and professional evaluation are required, and drug intervention and interventional treatment should be performed at the appropriate time.

To summarize, the foramen ovale itself should be in an open state during the fetal period, and "major fetal malformation screening" cannot diagnose patent foramen ovale; the foramen ovale that has not closed in the neonatal period can be closed at any time, and the child's heart ultrasound can be repeated six months or one year after birth; if the foramen ovale is still not closed after the age of 3, regular follow-up and evaluation are required, and drug intervention and interventional treatment should be performed at the appropriate time.