The correct answer is b- Alpha fetoprotein in maternal serum.

Open neural tube defects (NTD) are serious congenital malformations that result from the failure of the neural tube to close properly during embryonic development. These defects can lead to serious neurological problems, including paralysis, intellectual disability, and even death. The risk of NTD is increased in women who have a family history of the condition, who have previously had a child with NTD, or who have certain medical conditions such as diabetes.

Screening for NTD typically involves measuring the level of alpha fetoprotein (AFP) in maternal serum. AFP is a protein produced by the fetal liver and is normally present in the amniotic fluid and maternal serum. However, in cases of NTD, the AFP levels in maternal serum are significantly elevated.

The screening test is usually performed between 16 and 18 weeks of gestation and involves a simple blood test. If the AFP levels are elevated, further testing may be recommended, such as ultrasound or amniocentesis to confirm the diagnosis of NTD.

It is important to note that AFP screening is not a diagnostic test and can result in false positives or false negatives. Therefore, it is important to follow up with additional testing if the screening test is positive.

In summary, the screening of women at increased risk of carrying fetuses with open neural tube defects starts by performing alpha fetoprotein in maternal serum. This test is a simple and effective way to identify women who may be at increased risk of having a baby with NTD, allowing for early intervention and management.

References:

1. American College of Obstetricians and Gynecologists. (2018). Practice Bulletin No. 187: Neural Tube Defects. Obstetrics and Gynecology, 131(1), e82-e87.
2. Centers for Disease Control and Prevention. (2020). Neural Tube Defects (NTDs). Retrieved from https://www.cdc.gov/ncbddd/birthdefects/ntds.html.