An antenatal ultrasound done at 18-20 weeks of gestation is to detect:

Ans: A (Fetal anomalies) Ref: DC Dutta's Textbook of Obstetricsf pg: 98Explanation:Advantages of 18- 20 weeks scan during pregnancyDetailed fetal anatomy survey to detect any structural anomalies.Placental localization.USG examination is performed as a routine at 18-20 weeks to rule out fetal anomalies.o Open spina bifida and Arnold Chiari malformationBanana sign - flattening of cerebellar hemispheres.Lemon sign- scalloping of frontal bones,o Anencephaly - frog's eye appearance (absence of calvarium).Stomach bubble seen normally by 20 weeks. Absent stomach bubbie-esophageal atresia.Gastroschisiso Paraumbilical defect.o Not covered by membrane - herniated smalt bowel loops floating free in ammotie fluid..o Not associated with chromosomal anomalies, prognosis is good..Omphaloceleo Midline defect, cord inserted on the herniated mass,o Covered by membrane-hernia contains intestines, liver or both,o 40-60% associated with chromosomal anomalies, prognosis is poor.Advantages of First Trimester Scan During PregnancyDetects early pregnancyo An intrauterine gestational sac should be seen by:TVS when maternal serum Beta hCG level is 1000-1200 mlU/ml.TAS when maternal serum Beta hCG level is 6000 mlUJml.Confirms intrauterine pregnancy - to rule out Ectopic and Molar pregnancy.o Ectopic pregnancy features in USG - pseudo gestational sac sign, echogenic fluid in POD, ring of fire {Echogenic ring) in Doppler.o Molar pregnancy in USG - snow storm appearance.Confirms viability of fetus - cardiac activity should appear by 7 weeks in TAS and 6 weeks in TVS.Accurate dating - USG is the best method to estimate gestational ageo CRL (crown rump length) is the most accurate parameter in first trimester,o Accuracy in estimating GA iso +/- 1 week in 1st: trimestero +/- 2 weeks in 2nd trimestero +/- 3 weeks in 3rd trimesterNumber of fetuses.Identifies any uterine or adnexal pathology.Fetal nuchal fold thickness of > 3 mm by USG is a strong marker for chromosomal anomalies in 1S1 trimester between 11-13 weeks.Advantages of 3rd Trimester Scan During PregnancyEstimated fetal weight - by measuring FL, BPD. HC. AC.Fetal growth profile - Abdominal circumference {AC) is die single most important parameter for assessment of fetal growth.