Zoology · Ch 3 — Reproductive Health
Amniocentesis as a Diagnostic Procedure
Amniocentesis as a Diagnostic Procedure
Amniocentesis as a Diagnostic Procedure
Amniocentesis works by taking a small sample of the amniotic fluid that surrounds the foetus and testing it for chromosomal abnormalities. Because the amniotic fluid naturally contains cells shed from the foetus's own body, testing that fluid effectively tests the foetus itself without any direct contact.
The procedure is generally carried out between the 15th and 20th week of pregnancy: a long, thin needle is guided through the mother's abdomen and into the amniotic sac, under ultrasound guidance (see Fig. 3.1), to withdraw a small volume of fluid. This timing and method balance two needs — waiting long enough for there to be sufficient amniotic fluid and shed foetal cells to sample reliably, while still leaving enough of the pregnancy remaining to act on the result if a serious chromosomal abnormality is found. As covered in section 3.2, this same sampling procedure is what makes amn …
What this figure shows. A labelled cross-sectional diagram of a pregnant abdomen during an amniocentesis procedure. It shows, from outside in: the ultrasound transducer placed against the abdominal skin (used to guide the needle), the uterus as the outer muscular wall enclosing the pregnancy, the placenta attached to the inner uterine wall, the foetus floating within the uterine cavity, and the amniotic fluid surrounding the foetus, from which a thin needle (guided by the transducer) withdraws a small fluid sample. The diagram illustrates that the transducer and needle never contact the foetus directly — the fluid, not the foetus, is sampled — reinforcing the chapter' …