Best marker of gestational age in 2nd trimester is:

Ans. is a, i.e. Biparietal diameterRef Williams Obs. 24/e, p 198; USG in Obs. and Gynae by Callen 4/e, p 208"In the second trimester the BPD most accurately reflects the gestational age, with a variation of 7 to 10 day."Ref. Williams 24/e, p 198Prediction of fetal gestational age using ultrasound biometric parametersRef Bedside Obs/Gynae by Richa Saxena, p 191Period of gestationUltrasound parameter to be used8 weeks to 12 weeksCrown-rump length measurementSecond trimesterBPD, HCThird trimesterFemur lengthNote: In brachycephaly or Dolichocephaly - HC is better parameter in 2nd trimester than BPD as HC is unaffected by the shape of fetal head.