Teratogen Critical Period — MFDS Part 1 MCQ

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ModerateAnatomy (Head & Neck)Teratogen Critical PeriodMFDS Part 1

Teratogenic disruption of facial-prominence formation and fusion can produce cleft lip, with or without a cleft of the primary palate. During which embryonic period after fertilisation is this principally likely to occur?

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Reveal the answer and explanation

Correct answer: C — 4th to 8th week

Explanation lettering: D = shown as A · E = shown as B · A = shown as C · B = shown as D · C = shown as E

A is correct. The facial prominences responsible for the upper lip and primary palate develop and fuse during early embryogenesis, principally within weeks 4–8 after fertilisation. Disruption of their growth or fusion during this interval can produce cleft lip, with or without an associated primary-palate or alveolar cleft. Weeks 1–3 largely precede formation of the relevant facial prominences. Weeks 9–12 are important for continuing development and fusion of the secondary palate, so this interval would be relevant to cleft palate but is not the principal period for cleft-lip formation. By weeks 13–16 and 20–24, the principal morphogenetic fusion events have already occurred; exposure then is more likely to affect growth or functional maturation than cause a new cleft lip.

Reference: Yoon H, Chung IS, Seol EY, Park BY, Park HW. Development of the lip and palate in staged human embryos and early fetuses. Yonsei Medical Journal. 2000;41(4):477–484. https://www.gosh.nhs.uk/conditions-and-treatments/conditions-we-treat/cleft-lip-and-palate/