Answer: The correct answer is c- IgG.

Explanation: During pregnancy, the mother's immune system produces antibodies that can be passed on to the fetus through the placenta. Among the different types of immunoglobulins (Ig), only IgG can cross the placenta and provide passive immunity to the fetus. IgG antibodies provide protection against various infections, including measles, mumps, rubella, and hepatitis B. The transfer of IgG from the mother to the fetus starts around the 16th week of gestation and reaches its peak at around 34 weeks.

On the other hand, IgA antibodies are mainly found in mucosal secretions, such as saliva, tears, and breast milk, and do not cross the placenta. IgM antibodies are the first type of antibodies produced during an infection, but they are too large to cross the placenta. IgE antibodies are involved in allergic reactions and do not play a significant role in fetal immunity.

Regarding the second question, the L\S ratio (lecithin/sphingomyelin ratio) is a test used to assess fetal lung maturity. Lecithin and sphingomyelin are two phospholipids that are present in lung surfactant, a substance that helps to keep the lungs inflated and prevents collapse. The L\S ratio is calculated by measuring the relative amounts of lecithin and sphingomyelin in the amniotic fluid.

A ratio of 2.0 or higher is considered indicative of fetal lung maturity, while a ratio below 1.5 suggests immaturity. A ratio between 1.5 and 2.0 may be inconclusive and requires further testing, such as a fetal lung maturity test or a stress test. The L\S ratio is not the only test used to assess fetal lung maturity, and other factors, such as gestational age and clinical presentation, should also be taken into account.

References:

• American College of Obstetricians and Gynecologists. (2016). Practice Bulletin No. 172: Premature Rupture of Membranes. Obstetrics and Gynecology, 128(4), e165-e177. doi: 10.1097/AOG.0000000000001703
• American College of Obstetricians and Gynecologists. (2017). Practice Bulletin No. 181: Prevention of Rh D Alloimmunization. Obstetrics and Gynecology, 130(2), e57-e70. doi: 10.1097/AOG.0000000000002235
• American College of Obstetricians and Gynecologists. (2020). Practice Bulletin No. 222: Gestational Diabetes Mellitus. Obstetrics and Gynecology, 136(4), e49-e64. doi: 10.1097/AOG.0000000000004109
• American College of Obstetricians and Gynecologists. (2021). Practice Bulletin No. 226: Screening for Fetal Aneuploidy. Obstetrics and Gynecology, 137(1), e1-e17. doi: 10.1097/AOG.0000000000004226