Which of the following medications will be administered to assist with closure of patent ductus arteriosus (PDA) in premature infants?

Choice A rationale

Uterine atony, the failure of the myometrium muscle fibers to adequately contract after placental expulsion, is the most prevalent etiology of postpartum hemorrhage (PPH). These sustained contractions are essential to compress the endometrial blood vessels, effectively achieving hemostasis at the placental implantation site. Without adequate uterine tone, the vessels remain open, leading to excessive blood loss.

Choice B rationale

Labor augmentation, often achieved with oxytocin administration, is a risk factor for uterine atony, but it is not the direct, most common cause of PPH itself. While prolonged or over-stimulated labor can contribute to myometrial fatigue and subsequent atony, the mechanical failure of the uterus to contract effectively (atony) is the direct, primary cause in most cases.

Choice C rationale

Uterine inversion, a rare but life-threatening complication, occurs when the uterus turns partially or completely inside out. This profound anatomical displacement and associated uterine trauma cause immediate and massive hemorrhage, but its low incidence rate means it is not the most common cause of postpartum hemorrhage.

Choice D rationale

Cervical or vaginal lacerations can cause significant PPH, especially if associated with rapid delivery or instrumental assistance. This trauma results in bleeding from torn local vessels. While important, lacerations are less frequent than uterine atony as the overall primary cause of PPH, which generally accounts for about 70-80.

Choice A rationale

The absence of the enzyme hexosaminidase component A is the underlying defect in Tay-Sachs disease, a lysosomal storage disorder, not phenylketonuria (PKU). Tay-Sachs causes a buildup of GM2 ganglioside lipids in neurons, leading to progressive neurological deterioration, blindness, and spasticity, with symptoms typically presenting later than the described 5-month-old's developmental delay.

Choice B rationale

A chromosomal abnormality involving pairs 21 to 23 describes the genetic basis of Down syndrome (Trisomy 21) and other common trisomies, not PKU. Down syndrome is a set of physical and mental characteristics caused by an extra full or partial copy of chromosome 21, and its presentation is fundamentally different from the metabolic defect of PKU.

Choice C rationale

The absence of surfactant (a phospholipid-protein complex) in the lungs is the primary cause of Respiratory Distress Syndrome (RDS) in premature newborns. Surfactant reduces alveolar surface tension, preventing lung collapse. This defect is a pulmonary issue and bears no relation to the systemic metabolic disorder that affects the processing of the amino acid phenylalanine.

Choice D rationale

Phenylketonuria (PKU) is an autosomal recessive metabolic disorder caused by a deficiency of the liver enzyme phenylalanine hydroxylase (PAH). This enzyme normally converts the essential amino acid phenylalanine into tyrosine. Without adequate PAH, phenylalanine accumulates in the blood and brain, becoming toxic to the central nervous system, leading to the reported vomiting, eczema, and profound intellectual disability and developmental delay if untreated.