Correct Answer: A

Rationale: The correct answer is A: Cytosine with guanine. In the DNA double helix, cytosine always pairs with guanine forming a base pair, and adenine pairs with thymine. These complementary base pairs form the rungs of the ladder-like structure of DNA. Choice B, Rhodamine with biotin, is incorrect as they are not base pairs found in DNA. Choice D, Serine with tyrosine, is incorrect as they are amino acids, not DNA bases. Choice C, Diaminopurine with ribozyme, is also incorrect as ribozyme is an enzyme, not a base, and diaminopurine is not one of the standard bases found in DNA.

Correct Answer: D

Rationale: The correct answer is D. False labor contractions, also known as Braxton Hicks contractions, are typically irregular and do not lead to cervical dilation or effacement. They are often described as sporadic and temporary, becoming temporarily regular. Choices A, B, and C are incorrect because false labor contractions do not intensify with activity, do not cause cervical changes like dilation and effacement, and are not associated with the presence of a bloody show.

Correct Answer: D

Rationale: The correct answer is D. Cervical changes such as effacement and dilation to 2 cm are strong indicators of imminent preterm labor. These changes, combined with regular contractions, can signify labor at any gestation. Estriol can be detected in maternal plasma as early as 9 weeks of gestation. Levels of salivary estriol have been linked to preterm birth. Irregular, mild contractions occurring every 12 to 15 minutes without cervical change are generally not concerning. While the presence of fetal fibronectin in vaginal secretions between 24 and 36 weeks of gestation may predict preterm labor, its predictive value is limited (20%-40%). Therefore, cervical changes provide more reliable information regarding the risk of preterm labor.

Correct Answer: A

Rationale: The correct answer is A: A pattern of fetal late decelerations. Late decelerations during a contraction stress test are concerning as they indicate uteroplacental insufficiency, which can pose a risk to fetal well-being. Reporting this finding to the healthcare provider is crucial for prompt intervention. Choice B, fetal heart rate accelerations with fetal movement, is a reassuring sign of fetal well-being and does not raise immediate concerns. Choice C, absence of uterine contractions within 20 minutes, may require further assessment but is not as critical as late decelerations. Choice D, spontaneous rupture of membranes, is important but not the most immediate concern during a contraction stress test.

Correct Answer: A

Rationale: Rubella, also known as German measles, is a viral infection that can lead to severe birth defects when contracted by a mother during pregnancy. Rubella is the correct answer because it is specifically associated with causing birth defects such as deafness, intellectual disabilities, blindness, and heart disease in the embryo. Syphilis (Choice B) can be passed from mother to fetus but does not cause the mentioned birth defects associated with Rubella. Cystic fibrosis (Choice C) and Phenylketonuria (Choice D) are genetic conditions and not infections transmitted from mother to fetus, making them incorrect choices in this context.