A nurse explains fetal viability. What gestational age range is a fetus considered to be viable?
Around 20-25 weeks
At term
At 30 weeks
Begins at 12 weeks
The Correct Answer is A
Fetal viability is the gestational age at which a neonate has a reasonable chance of extrauterine survival with intensive medical support. This threshold is primarily determined by the pulmonary maturation and the development of the terminal air sacs for gas exchange. Survival rates increase significantly as the fetus approaches the third trimester.
A. Around 20-25 weeks: This range represents the current limit of viability where neonatal intensive care can occasionally support life outside the womb. Success depends heavily on the administration of antenatal corticosteroids and advanced ventilatory technology. It marks the transition from pre-viable to potentially viable status.
B. At term: Viability is reached much earlier than the 37-week definition of full term. While term infants have the highest survival rates and lowest morbidity, the viability threshold is a much earlier milestone in fetal development. Defining viability as term would ignore the capabilities of modern neonatology.
C. At 30 weeks: By 30 weeks, most fetuses are considered highly viable with a survival rate often exceeding 90%. However, this is not the point where viability "begins," as many infants survive if born several weeks earlier. This choice overlooks the critical window between 23 and 26 weeks.
D. Begins at 12 weeks: At this early stage, the lungs are in the pseudoglandular phase and are incapable of any gas exchange. The fetus lacks the skin integrity and organ maturity necessary to survive outside the intrauterine environment. Survival is physiologically impossible at this gestational age.
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Related Questions
Correct Answer is B
Explanation
Fetal engagement occurs when the biparietal diameter of the fetal head passes through the pelvic inlet into the true pelvis. This is clinically identified when the presenting part reaches the level of the maternal ischial spines, designated as 0 station. It signifies that the fetal head is no longer ballotable.
A. Birth is complete: Delivery of the neonate is only finalized when the entire body has exited the vaginal canal, followed by the third stage of labor. A 0 station indicates the fetus is only at the mid-pelvic level. Significant expulsive effort and descent are still required for birth.
B. Engagement: Reaching 0 station confirms that the widest part of the head has successfully entered the pelvic cavity. In nulliparous clients, this often occurs before the onset of labor, while in multiparous clients, it may happen during the active phase. It is a key pelvic landmark.
C. Placenta delivery: The third stage of labor involves the detachment and expulsion of the placenta after the fetus is born. This occurs well after the fetus has passed the 0 station and the vaginal introitus. It is unrelated to the mechanical station of the fetal head.
D. Full dilation: Dilation refers to the opening of the cervix to 10 centimeters and is an assessment of the birth canal rather than fetal position. While engagement often coincides with progress in labor, a client can be at 0 station without being fully dilated. They are independent clinical measurements.
Correct Answer is D
Explanation
Vernix caseosa is a white, cheese-like substance composed of sebum and desquamated epithelial cells that coats the fetal skin. It functions as a biofilm that provides antimicrobial protection and prevents transepidermal water loss. It is essential for thermoregulation and skin maturation in the aqueous intrauterine environment.
A. Oxygen transport: Oxygen delivery to the fetus is exclusively managed by the umbilical vein and fetal hemoglobin. Vernix caseosa is an external cutaneous coating and has no role in respiratory gas exchange. It does not interact with the vascular system.
B. Hormone production: Hormonal synthesis during pregnancy is primarily the responsibility of the placenta, fetal adrenal glands, and maternal endocrine organs. Vernix is a mechanical barrier and lubricant. It does not possess the glandular tissue required for endocrine secretion.
C. Bone development: Skeletal mineralization is dependent on the transport of calcium and phosphorus across the placenta. Vernix caseosa only affects the integumentary system and does not influence the ossification of fetal bones. Bone health is a metabolic process, not a cutaneous one.
D. Protects the fetal skin from amniotic fluid: The primary role of vernix is to act as a waterproof barrier, preventing the fetal skin from becoming macerated by prolonged exposure to amniotic fluid. It also facilitates passage through the birth canal by acting as a natural lubricant during delivery.
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