Crown rump length (CRL) is a measure of foetal growth, with a reduction indicating reduced foetal development. Based upon this what can you conclude about the two experiments?

Question

BlackTom AI · Accepted Answer

To approach this question, I’ll lay out what each statement is asserting and then assess its plausibility in light of the topic: crown rump length (CRL) as an index of foetal growth and the implications for fetal development in different pregnancy contexts.

Option 1: Overall reduced muscle weights were associated with reductions in hypertrophy more than hyperplasia.
- This statement discusses patterns of muscle development (hypertrophy vs hyperplasia) in relation to reduced muscle weight. It suggests that, when muscle weight is reduced, the diminution is driven more by decreases in muscle fiber size (hypertrophy) than by a reduction in the number of fibers (hyperplasia). This is a general principle about muscle development, not specifically tied to twin pregnancies or seasonal effects. It could be true in some contexts, but without data linking CRL-based fetal growth reductions to whether hypertrophy or hyperplasia is more affected, its relevance to the twin-versus-season question is indirect. Therefore, this option speaks to a general mechanism rather than a direct consequence of twin pregnancies, making it less certain as evidence for the specific conclusions about twins.

Option 2: Twin pregnancies are more likely to inhibit myogenesis.
- This aligns with the idea that twin pregnancies impose greater resource competition for the fetus (shared placental circulation, limited nutrients, reduced uterine space). A reduction in the formation of muscle fibers (myogenesis) in twins is a plausible outcome if the intrauterine environment is constrained. Therefore, this statement directly supports a conclusion that twins can reduce myogenesis, and it is logically consistent with CRL indicating limited growth.

Option 3: Twin pregnancies placed a greater maternal constraint than the effect of season.
- Here, the claim is that the intrauterine constraints associated with carrying twins exceed the additional constraints that could be introduced by seasonal factors (such as ambient temperature, maternal nutrition variability, etc.). If twins inherently impose stronger constraints on fetal development than seasonality does, this would explain why twin-related effects dominate over seasonal effects on growth measures captured by CRL. This is a coherent and testable contrast and fits a narrative where twin pregnancies have a larger impact on fetal development than seasonal variation.

Option 4: Reduced myogenesis will be associated with reduced skeletal size.
- Conceptually, if myogenesis is reduced (fewer muscle fibers formed), one would expect some downstream effect on skeletal size, since muscle development contributes to overall skeletal growth and proportion. However, skeletal size is influenced by multiple processes (bone growth, cartilage development, and muscle forces). So while reduced myogenesis can contribute to smaller skeletal dimensions, the relationship is not exclusive or absolute. This statement is plausible and consistent with the idea that impaired muscle formation can accompany smaller skeletal structures, but it presumes a direct and primary link that may not always hold, depending on compensatory growth later in development.

In summary, option 1 discusses a general pattern about hypertrophy vs hyperplasia that is not specifically anchored to twin versus season effects, making it a weaker direct support for the question’s conclusion. Options 2 and 3 offer direct, mechanism-based explanations that twin pregnancies have stronger inhibitory effects on fetal muscle development (myogenesis) and that these twin-related constraints can surpass seasonal influences, which makes them coherent with the CRL-based interpretation. Option 4 describes a plausible consequence of reduced myogenesis but rests on a broader causal chain that may vary with context and compensatory growth.

MERGE_2025_0317 Tutorial 1: muscle fibre dynamics and animal growth

Crown rump length (CRL) is a measure of foetal growth, with a reduction indicating reduced foetal development. Based upon this what can you conclude about the two experiments?

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