33.     Human Chorionic Gonadotrophin.  

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MCQ Paper 1

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a. is mainly produced by the granulosa cells False
b. peak levels occur at twenty weeks False
c. shares the same alpha chain with FSH and LH True
d. levels are low in trisomy 21 False
e. levels are raised in trisomy 18 False
f. can be used to induce ovulation True
g. is elevated in cases of hydatidiform mole and choriocarcinoma True
h. is elevated in cases of multiple pregnancy True
i. is elevated in hyperemesis gravidarum True
j. is elevated in ectopic pregnancy False
k. is a marker for ovarian cancer False
l. is a marker for chronic hepatic disease and hepatoma False

HCG, not surprisingly, is only produced in the chorion.

The granulosa cells surround the developing ovum during the menstrual cycle and produce oestradiol.

The level of HCG peaks at 8 - 12 weeks.

This is associated with lessening of vomiting in pregnancy from this time.

Also, HCG stimulates the ovary and may be involved in the presence of simple ovarian cysts in early pregnancy.

As the levels fall, such cysts often subside and this is one of the reasons for not rushing in to remove simple cysts in the first trimester.

It is also feared that such surgery would increase the risk of miscarriage.

The effect of HCG on the ovary also explains the association between:

    hydatidiform mole (see MCQ6, question 19), with marked elevation of HCG,

    and ovarian cyst formation - theca lutein cysts.

All of the gonadotrophins share the same alpha chain. HCG and LH are chemically very similar.

So HCG can be used to mimic LH and induce ovulation.

The chemical changes associated with trisomy 21 are best remembered by simply taking on board that:

    these pregnancies behave as though immature.

At 16 weeks, when testing is usually done, the levels of HCG, oestriol and MSAFP are similar to those of normal pregnancy of 12 - 14 weeks.

HCG peaks by 12 weeks, so the level is falling at 16 weeks.

In trisomy 21, it remains elevated, compared with normal pregnancy.

Similarly, oestriol and MSAFP levels, which continue to rise during the second trimester, are low in Down's syndrome.

Trisomy 18 is associated with low levels of all three markers.

This is a unique pattern and associated with a 1:16 risk of trisomy 18.

Screening for Downís syndrome is about to change.

The Uk National Screening Committee has recommended that 1st. trimester combined screening become the standard test.

It consists of measurement of nuchal translucency and free beta-hCG and PAPP-A in the first trimester.

(See MCQ 3, question 36 and MCQ 10, question 35.)

Second trimester biochemical screening will remain for the estimated 15% of women who book too late for the 1st. trimester test.

Levels tend to be lower than normal with ectopic pregnancy and not to double at the usual rate.

Ca125 is the marker for ovarian cancer.

AFP may be elevated in chronic liver disease and hepatoma.

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Return to MCQ 4, answer 26. "Screening for DS"
Return to MCQ 2, answer 9. "Miscarriage"
Return to MCQ 5, answer 22. "Hyperemesis"

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