It is a typical plot in the series when the preganancy outcome is endangered, the husband’s family would prioritize the fetus while the wife’s family would prioritize the mother. Biologically, the intrinsic contradiction comes from two designs: sexual reproduction and viviparity with invasive placenta.
In sexual reproduction, the offspring’s genetic materials (DNA) is sourced from gamates of multiple donors. Humankind reproduces as a diploidy kind of sexual reproduction, where the fuse of two gamates results in the offsprings’ genetic materials being composed of two strands of DNA from two donors we called maternal and paternal respecitively. The reading out of DNA needs the transcription machines, which can only transcribe from one DNA strand. If the two strands of DNA are exactly semestic, there will be not dicernable at all whether the machine is transcribed from one strand or another. If, some parts of the strands have systematic divergence in the transcribed outputs, at some point the power of nature selection would show up and the transcription from which strand would be less random.
There is, indeed, the systematic divergence in some genetic regions called genomic imprinting. In human genome, there are ~228 imprinting genes reported. That means these genes are transcribed from only the paternal or the maternal DNA. The functional analysis gave rise to the hypothesis that the tug-o-war started at this point. The genes transcibed from the paternal DNA would like the fetus to invade deeper into the maternal body to get more nutrients and grow larger. While the genes transcribed from maternal DNA is to confine the fetal growth.
For example, Igf is normally only transcribed from the paternal side while the receptor Igfr is only transcribed from the maternal side. IGF2 promotes growth of the placenta whereas IGF2R restricts this growth by mopping up excess IGF2 protein so there will be less of it available. If the imprinting of the maternal strand is disrupted, the IGF2 is expressed too much, the children will have Beckwith–Wiedemann Syndrome and be over-large and are prone to develop cancer early in life.
Another example is the Paternal Expressed Gene 3 ( PEG3 ) which is expressed in the placenta and hypothalamus. This gene is transcribed from the paternal side and push the mothers to nurture the newborn. This co-expressed and co-influed by the same gene to the fetal hypothalamus and maternal hypothalamus is thus to confer a transgenerational propagation and it’s hypothesized that the paternal-expression renders more benefit in propagation rate. If Muslims are pregnant during the ramadan, they have smaller placentas. This is in line with the observation in mouse models that in starvation, the PEG3 is not expressed in placenta but still expressed in the fetal hypothalamus. The placenta then start to devour themselves to feed the fetus.
All these imprinting genes are playing their role in the conflicting between the mathers and the father’s interests.
