The optimal gestational age to examine fetal anatomy and measure nuchal translucency in the first trimester

Abstract

The objective of this study was to determine the optimal gestational age for examining fetal anatomy and nuchal translucency in the first trimester. In a prospective cross-sectional study, 1288 women from an unselected population underwent a detailed assessment of fetal anatomy at 10-14 weeks of gestation (confirmed by crown-rump length) with the use of transabdominal sonography and transvaginal sonography, when necessary. Visualization of fetal anatomy improved with increasing gestational age: 6, 75, 96, and 98% of cases could be visualized at 10, 11, 12 and 13 weeks of gestation, respectively, and was similarly high (98%) at 14 weeks. The ability to measure nuchal translucency was similar from weeks 10 to 13 (100, 98, 98 and 98% success rate), but fell to 90% at 14 weeks. The need for transvaginal sonography steadily decreased with increasing gestational age, being 100, 42, 21, 15 and 11% at 10, 11, 12, 13 and 14 weeks, respectively. From these data it appears that the optimal gestational age to examine fetal anatomy and measure nuchal translucency in the first trimester is 13 weeks.

First‐Trimester Sonographic Diagnosis of Holoprosencephaly

“…According to a previous study, the cranium, thalamus, choroid plexus, and lat-eral ventricles can be visualized sonographically in 90% of cases at 11 weeks and in virtually all cases between 12 and 14 weeks. 15 The choroid plexuses of the lateral ventricles are very prominent organs during this developmental period. They can be easily identified by sonography, which can provide an important landmark for normalcy of the fetal brain at this early gestational age.…”

The value of screening for major fetal abnormalities during the nuchal translucency examination

“…Studies show that examination of non‐cardiac anatomy at 11–14 weeks – skull, brain, face, spine, stomach, abdominal wall, kidneys, bladder and extremities – can be achieved in 75–98% of cases with visualisation improving with increasing gestational age 5 , 6 , 7 .…”

“…The optimal age for examining anatomy is from 12+0–13+6 weeks 5 , 6 , 7 with 13 weeks being the optimal gestation for combining fetal anatomy examination with the NT measurement 7 . The fetal heart is the most difficult organ to visualise consistently 11 .…”

“…There are many advantages to examining fetal anatomy in the first trimester: Early detection of an abnormality allows more time to investigate and decide upon appropriate management and treatment optionsIf a severe structural abnormality is detected then termination may be offered without the need for further invasive tests such as chorionic villus sampling or amniocentesisIt allows the option of an early versus late termination of pregnancy with a resulting decrease in surgical complications and psychiatric morbidity 7 It may help to protect a patient's privacy if they choose to terminate as the pregnancy is generally not physically obvious at this stage and many couples choose to delay announcement until the completion of the first trimesterIt may identify fetuses with abnormalities, which would miscarry spontaneously, providing an opportunity to investigate the cause of the abnormalities, for example by karyotyping 10 The reassurance of normality is beneficial, especially in pregnancies that are high risk.There are limitations in scanning for abnormalities in the first trimester which may influence the results achievable. These include:…”

“…It allows the option of an early versus late termination of pregnancy with a resulting decrease in surgical complications and psychiatric morbidity 7 …”