Final answer:
The suggested screening test for an 18-week pregnant woman at the age of 30 is Maternal serum alpha-fetoprotein (MSAFP) screening, which can detect neural tube defects and chromosomal abnormalities.
Step-by-step explanation:
The appropriate screening test for a 30-year-old gravida 3, para 2-0-0-2 at 18 weeks of gestation is c. Maternal serum alpha-fetoprotein (MSAFP) screening. This test helps in identifying potential defects such as neural tube defects and chromosomal abnormalities like trisomy 21, which has a higher incidence as maternal age increases. Considering the mother's age, it is also wise to consider the potential for genetic counseling or additional screenings if there is a family history of genetic disorders or if either parent is at an advanced age, as per recommendations.
Although a biophysical profile (option a) is useful later in pregnancy, and chorionic villi sampling (option b) is conducted earlier, the MSAFP is a standard screening at this point in gestation. Screening for diabetes mellitus (option d) is also important but typically occurs later in pregnancy unless the patient has risk factors warranting earlier screening.