Interpretation
Alterations in the functionality of the abdominal muscles resulting from
pregnancy-induced morphological changes have long been
known25, and it has been proposed that women with
stronger abdominal muscles might push more effectively, shortening the
second stage of labor26. A prolonged second stage has
been associated with adverse birth outcomes, including a greater risk of
perinatal asphyxia27. However, in the present work, no
association was seen between any abdominal muscle thickness and the
duration of labour. This suggests that the improved CB gas values
observed in offspring born to women with greater abdominal wall muscle
thicknesses is due to metabolic rather than structural mechanisms.
Uterine contractions during labour induce metabolic stress in the
foetus, which is reflected in CB gas values at
birth28.
In the present work, the subjects with a thicker EO at rest had newborns
with less acidic cord arterial blood, which agrees with the association
seen between a greater EO thickness during activation and a better
1-minute Apgar test score. Reductions in the pH of the arterial CB are
generally related to acute labour difficulties, such as an acute
occlusion of the umbilical cord.29
Acidosis in the umbilical artery can lead to vasoconstriction in the
peripheral tissues (mostly) of the foetus30.
Importantly, the present results suggest that babies born to mothers
with greater abdominal muscle thicknesses are better oxygenated, as
shown by the venous CB in particular; gas values measured in the venous
CB reflect the concentration of oxygen originally provided to the
fetus29. The mother’s skeletal muscle might play a
role in the oxygenation of the cord blood via the release of myokines,
which could cause vasodilation in the placental blood
vessels31. Certainly, the myokines released by muscle
tissue are known to protect against ischemia in
angina32. Although no study has specifically
examined the association between maternal myokines and birth outcomes, a
systematic review33 suggests that myokines may act as
signalling molecules between maternal skeletal muscle and the placenta,
regulating maternal–foetal blood flow. Further studies on myokine
levels and their association with abdominal muscle thickness in pregnant
women are needed to better understand the mechanisms behind the present
findings.
A greater IRD, both at rest and during crunches, was related to a higher
PCO2, a lower PO2, and lower oxygen
saturation in the arterial CB, and a more acidic pH for the venous CB.
In addition, neonates born to mothers with a higher IRD during crunches
had a lower venous CB oxygen saturation. These results confirm that a
smaller IRD is associated with greater oxygenation of the foetus at
birth. However, no association was seen between the IRD and any other
birth outcomes, such as the Apgar test score or the duration of labour.
This agrees with that described by Oliveira et al.12In contrast to the present findings, the latter authors found no
association between IRD and CB pH or
PCO212. These differences might be
attributable to the fact that the latter study involved a smaller sample
(n=24).
No cut-off has been established for diagnosing rectus diastasis in
pregnant women. Indeed, the literature quotes the use of cut-off points
at 2 cm above the umbilicus ranging from 20 to 86
mm19,34,35. For this reason, and following the
criterion used in a previous study35, the IRD
50th percentile was used in the present work as a
cut-off to explore whether there was any relationship between IRD and
birth outcomes. Most of the previously discussed associations with IRD
were maintained only for women with an IRD above the median during
crunches. Being above the median was also associated with poorer CB gas
values, but not with the rest of the studied birth outcomes. Although
the literature contains no studies with which to reliably compare the
present results, the finding of the above associations during crunches
could be clinically important. Maternal pushing during the second stage
of labour usually involves crunching to assist the baby’s descent
through the birth canal. Therefore, the ability to reduce the IRD at
this stage might be decisive in improving the oxygenation of the foetus.
Further studies exploring the influence of core exercises during
pregnancy on the above-described outcomes are needed.