Senior Consultant, Fetal Medicine, Artemis Hospitals, Gurgaon, India
Part 4 of 7 in Diagnostic Utility of First Trimester Ultrasound
Structural Abnormalities the First-Trimester Scan Can Already Catch
June 21, 2026
Every scan should be treated as an anomaly scan, Dr. Sablok says: the era of waiting until 20 weeks to look for structural problems is over. Acrania/anencephaly, alobar holoprosencephaly, abdominal wall defects like exomphalos and gastroschisis, megacystis and absent limbs are all reliably detectable even in the first trimester. Conditions like microcephaly, agenesis of the corpus callosum, and open spina bifida generally can't be confirmed until the relevant structures have formed further, around 20-22 weeks.
She describes real cases from her practice: anencephaly diagnosed at 11 weeks 5 days; a rare iniencephaly with the 'star-gazing sign' (incidence roughly 1 in 50,000) on 3D ultrasound; open spina bifida diagnosed at 13 weeks 5 days; a skeletal dysplasia with femur bowing caught at 13 weeks 3 days; a twin pregnancy where septations behind the head revealed monosomy X (Turner syndrome); and a case of conjoined twins, all identified on the first trimester scan alone.
This guide is based on a live Jivo Masterclass — Dr. Aanchal Sablok taught doctors across Africa on June 21, 2026.
FROM THE LIVE Q&A
How does the stage of CKD (chronic kidney disease) affect the risk of preeclampsia?
Dr. Aanchal Sablok
If the mother already has chronic kidney disease, she is already at risk of chronic hypertension. When placental implantation occurs on top of this background, the relevant terminology is preeclampsia superimposed on chronic hypertension. This represents an even higher risk of developing preeclampsia, particularly in the presence of chronic renal disease, chronic hypertension, or other conditions such as autoimmune disease. The risk of fetal growth restriction (small for gestational age) is also correspondingly higher in this group.
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Frequently Asked Questions
Which structural abnormalities can already be detected on a first trimester scan?▼
Acrania and anencephaly, alobar holoprosencephaly, abdominal wall defects such as exomphalos and gastroschisis, megacystis, and absent limbs are all reliably detectable even in the first trimester.
Which conditions cannot be confirmed until later in pregnancy?▼
Conditions such as microcephaly, agenesis of the corpus callosum, and open spina bifida generally cannot be confirmed until the relevant structures have formed further, around 20 to 22 weeks.
How early has open spina bifida been diagnosed on ultrasound?▼
In one case described, open spina bifida was diagnosed at 13 weeks 5 days.
What is the star-gazing sign and how rare is the condition it indicates?▼
The star-gazing sign appeared on 3D ultrasound in a case of iniencephaly, a rare neural tube defect with an incidence of roughly 1 in 50,000.
Can chromosomal conditions be picked up incidentally during a structural scan?▼
Yes. In one twin pregnancy, septations behind the head on a structural scan revealed monosomy X (Turner syndrome), illustrating how structural and chromosomal findings can surface together on the same scan.
In This Series: Diagnostic Utility of First Trimester Ultrasound
- 1.Diagnostic Utility of First Trimester Ultrasound
- 2.Screening for Down Syndrome: How Detection Rates Evolved From 30% to 96%
- 3.Nuchal Translucency: Why a High Reading Doesn't Mean What Patients Fear
- 4.Structural Abnormalities the First-Trimester Scan Can Already Catch
- 5.Preeclampsia Screening: Uterine Artery Doppler, PLGF, and the New Role of the Ophthalmic Artery
- 6.Predicting Preterm Labour: Why Cervical Length Should Be Measured at 12 Weeks
- 7.The Inverted Pyramid of Care: Rethinking When Pregnant Women Should Be Seen