INTRODUCTION
The abdominal musculature undergoes morphological and functional changes
during pregnancy1. For instance, the inter-recti
distance (IRD) increases, especially in the third
trimester2, while other stabilizing muscles of the
lumbar spine, such as the transverse abdominis (TrA) and the internal
oblique (IO) and external oblique (EO)3 muscles, tend
to become thinner as pregnancy progresses4. A number
of studies have explored the associations shown between such changes in
the abdominal muscles during pregnancy, and lower back
pain4, pelvic symptoms5, and quality
of life6, and with pelvic floor
status7 in the postpartum period. Others have focused
on the role of pelvic floor muscles on birth
outcomes8. However, despite the fact that the
abdominal muscles play an important role during
labor9, little is known about their influence on
birth-related outcomes.
The second stage of labour begins with the full dilation of the cervix
and ends with the birth of the baby. It includes a passive phase, in
which the descent of the foetus takes place, and an active phase, during
which the mother voluntarily pushes the foetus through the birth
canal10. The successful delivery of the baby therefore
depends on both uterine contractions and maternal abdominal
effort9. Excessive stretching of the abdominal muscles
during pregnancy has been previously associated with a reduction in
contractile strength11, and interestingly, a larger
diastasis recti has been associated with poorer electromyographic
readings for the rectus abdomini muscles during
labour12.
There are other pathways, however, via which maternal muscle status
might influence birth outcomes. For example, muscles also have an
important endocrine function via the secretion of myokines that can
improve vascular endothelial function13, perhaps
leading to better placental and umbilical cord blood (CB) flow during
birth. Thicker abdominal muscles might, therefore produce more myokines,
further improving these variables.
The aim of the present work was to explore the associations shown by the
thickness of abdominal muscles and the IRD at the 34thweek of gestation (w.g.), with the duration of the first and second
stages of labour, the neonatal Apgar test score, and umbilical CB gas
values at birth.