The overall number of cases of STIs is:

Choice A reason: Herpes simplex virus is incorrect because it is not the infection described in the question. It is transmitted through direct contact with the skin or mucous membranes of someone who is infected, usually through oral or genital sex. Symptoms include painful blisters and sores in the mouth or genitals. It does not cause life-threatening infections, but it can increase the risk of other sexually transmitted infections.

Choice B reason: Human papillomavirus is incorrect because it is not the infection described in the question. It is transmitted through direct contact with the skin or mucous membranes of someone who is infected, usually through genital sex. Symptoms include genital warts and cervical cancer. It does not cause life-threatening infections, but it can increase the risk of other cancers.

Choice C reason: Human immunodeficiency virus is correct because it is the infection described in the question. It is transmitted through direct contact with the blood or body fluid of someone who is infected, usually through unprotected sex, sharing needles, or passed from a mother to a baby at birth. Symptoms may take 10 years or more to show. Once they appear, the person is susceptible to life-threatening infections, such as pneumonia, tuberculosis, or cancer. This condition is also known as acquired immunodeficiency syndrome (AIDS).

Choice D reason: Cytomegalovirus is incorrect because it is not the infection described in the question. It is transmitted through direct contact with the saliva, urine, or breast milk of someone who is infected, usually through kissing, sexual contact, or breastfeeding. Symptoms are usually mild or absent in healthy people, but they can be serious in people with weakened immune systems or unborn babies. It does not cause life-threatening infections, but it can cause birth defects, hearing loss, or vision problems.

Choice A reason: Infection is not a common cause of IUGR, as most infections do not cross the placenta and affect the fetal growth. However, some infections such as cytomegalovirus, rubella, or toxoplasmosis can cause congenital anomalies and IUGR.

Choice B reason: Previous preterm birth is not a direct cause of IUGR, as it does not affect the current pregnancy. However, it may indicate an underlying maternal or fetal condition that could increase the risk of IUGR, such as cervical incompetence, placental abruption, or preeclampsia.

Choice C reason: Utero-placental insufficiency is the most common cause of IUGR, as it reduces the blood flow and oxygen delivery to the fetus. It can result from maternal factors such as hypertension, diabetes, smoking, or drug abuse, or from placental factors such as placenta previa, placental infarction, or cord compression.

Choice D reason: Chronic hypertension is a risk factor for IUGR, as it can lead to utero-placental insufficiency and fetal hypoxia. However, it is not the only cause of IUGR, as other factors can also affect the placental function and fetal growth.