Is it a boy or a girl? This is one of the first questions asked by a new mom-to-be. Until recently, the ultrasound was the only non-invasive, scientific way to learn the gender of the unborn baby. Other highly accurate methods such as chorionic villus sampling (CVS) and amniocentesis (“amnio”) are invasive, carry a risk to the mom and/or baby and are only prescribed by a doctor for older moms or for pregnancies with risk of genetic disorders.

The Pink or Blue® test is a new, non-invasive DNA-based gender test based on detecting small amounts of the baby’s DNA in the expectant mother’s blood. If small amounts of the Y-chromosome are detected, then the baby is a boy. If no significant amount of Y-chromosomal DNA is detected then the mom is expecting a baby girl.

Many questions arise about ultrasounds and gender detection:
1. How early can an ultrasound scan show the gender of the fetus?
2. How accurate is the gender prediction from an ultrasound?

Before we can answer those questions, we must first understand what an ultrasound is.

What is an ultrasound?

An ultrasound (also called sonogram) scan uses high frequency, low power, sound waves sent through the mom’s belly into the uterus. As these energy waves encounter internal surfaces (uterus, placenta, fetus) they bounce back and are detected by the scanner. The amount of ultrasound waves bouncing back varies as the surface which they hit changes e.g. folds, texture, and density. The computer monitor uses this information to generate a picture of the fetus and its environment which can be viewed on the monitor.

The ultrasound image can be used to measure the size of the baby to assess its development and growth. The ultrasound is used to detect certain fetal developmental abnormalities such as cleft palate, Down Syndrome, spina bifida, cardiac anomalies, and other physical malformations.

Ultrasound and Gender Detection

Gender is determined by visually inspecting the ultrasound image for the genital tubercle (developing reproductive tissues) in the first trimester, or penis/labial folds in later stages of pregnancy. The accuracy of this method of gender determination depends on the position of the baby as well as the skill of the technician performing the scan. Several studies have been conducted to determine the accuracy of gender prediction at different stages of pregnancy.

Here are brief summaries of a few of these studies:

Michailidis et. al. “The use of three-dimensional ultrasound for fetal gender determination in the first trimester.” Br J Radiol. 2003

• Study included 200 participants in the first trimester; 2 technicians independently reviewed the ultrasound data to determine gender
• gender was determined in 81.5% of participants (18.5% inconclusive rate)
• In cases where both examiners agreed on gender determination, they were 85.3% accurate.
• Of the 14.7% error rate: 6.7% were cases where both examiners predicted the incorrect gender, and 8% were cases where one of the examiners predicted the wrong gender.

Adeyinka et. al. “Ultrasonographic assessment of fetal gender” Afr J Med Med Sci. 2005.

• Study included 415 participants ranging from 15-40 weeks gestation
• Gender was determined in 87.5% of participants (12.5% inconclusive rate)
• 90.6% of female predictions were correct while 83.2% of male predictions were correct

Efrat et. al. “Fetal gender assignment by first-trimester ultrasound.” Ultrasound in Obstetrics and Gynecology. 2006.

• Study included 656 participants ranging from 12-14 weeks gestation
• Gender was determined in 93% of participants (7% inconclusive rate)
• At 12 weeks, 99% of male gender predictions were correct, and 91% of female predictions were correct
• At 14 weeks, 100% of both male and female predictions were correct
  

Hsiao et. al. “Fetal gender screening by ultrasound at 11 to 13(+6) weeks.” Acta Obstet Gynecol Scand. 2008

• Study included 496 participants who were 11-14 weeks gestation
• Gender was determined in 89% of participants (11% inconclusive rate)
• A t 11 weeks gestation, gender predictions were 71.9% accurate, at 12 weeks accuracy was 92%, while at 13 weeks the accuracy increased to 98.3%

The results of these and other studies vary greatly, and no general consensus exists on an overall accuracy rate for ultrasound gender detection. The inconclusive rate for gender determination is also quite high. Many message boards can be found online with confused expectant moms who try to read each other’s ultrasounds after a technician was hesitant to assign a gender to the fetus. Many messages can also be found from women who received conflicting ultrasound results on subsequent visits, or found out in the delivery room that multiple ultrasounds had been wrong.

It is important to go into an ultrasound with proper expectations. The real usefulness of the ultrasound is in determining the overall health of development of the baby. The gender prediction made at an ultrasound scan, especially one performed early in the pregnancy, should not be assumed to be 100% correct.

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