**Core Concept**
The safe motherhood schemes (SMS) aim to reduce maternal and infant mortality by addressing the main causes of death, which include hemorrhage, sepsis, obstructed labor, and hypertensive disorders. The major thrust area is focused on improving the quality of care during pregnancy, childbirth, and postpartum periods.

**Why the Correct Answer is Right**
The correct answer focuses on improving the quality of care during pregnancy, childbirth, and postpartum periods. This is achieved by providing essential obstetric care, including antenatal care, skilled attendance at delivery, and postnatal care. Antenatal care includes regular check-ups, screening for diseases, and education on pregnancy and childbirth. Skilled attendance at delivery ensures that complications are promptly identified and managed. Postnatal care focuses on preventing postpartum hemorrhage, providing family planning education, and promoting breastfeeding.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specifically address the quality of care during pregnancy, childbirth, and postpartum periods, which is the main focus of safe motherhood schemes.
**Option B:** This option is incorrect because it mentions family planning, which is an important aspect of reproductive health but not the primary focus of safe motherhood schemes.
**Option C:** This option is incorrect because it mentions nutrition, which is an important aspect of maternal and child health but not the major thrust area of safe motherhood schemes.

**Clinical Pearl / High-Yield Fact**
The World Health Organization (WHO) recommends that every pregnant woman receive at least four antenatal check-ups, including one in the first trimester, one in the second trimester, and two in the third trimester.

**Correct Answer: D**