Switch over from fetal to adult Hb

At what gestational age switch over from fetal to adult hb synthesis begins? 
a.30 weeks 
b.36 weeks 
c.7 days post natal 
d.3 weeks post natal

ANSWER:

Ans here is 30 wks and NOT 36wks... If 20 wks was in options then the ans would be 20 wks.... many MCQ books give the wrong answer to it....
CORRECT POINTS ARE ---
1.After the first 8 weeks of development, the fetus' primary form of hemoglobin switches from embryonic hemoglobin to fetal hemoglobin....
2.Fetal Hb to Adult Hb SWITCHOVER BEGINS at 20 wks Intrauterine...
3.Significant switch over to adult Hb at 30 wks Intrauterine...
4.Adult Hb levels attained at 7 months of LIFE...
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