Results
Two hundred and seventy-four women were invited, and 264 (95%) women
agreed to participate. Of the ten women (5%) who declined to
patriciate: six women did not provide any reason, one reported in pain,
one was not interested and two declined because their partner did not
want the women to participate. Two hundred and twenty-six women
delivered vaginally. Two hundred and nineteen were nulliparous, six
(2.7%) had had a previous caesarean section and one (0.5%) had had two
previous caesarean sections (none of which were in the second stage of
labour). One hundred and twenty-one (53.5%) perineal tears were
examined by midwives and 105 (46.5%) by doctors (Table 1). Twelve
(4.6%) women had an intact perineum, eight (3%) a first-degree tear
and 185 (70.3%) a second degree tear. Twenty-one (9.3%) women
sustained OASIs: eight (3%) a 3a tear and 13 (4.9%) a 3b tear. Of
these, five women were examined by midwives who missed four (80%)
(Table 1) and sixteen were examined by doctors who missed two (12.5%)
OASIs (Table 2).
Two hundred and eighteen of the 226 (96%) women had ultrasound images
that were of a suitable quality for analysis. In 21 (9.6%) women an
anal sphincter defect was identified by TPUS. Table 3 shows the
correlation between ultrasound and clinical findings. Of the 21 OASIs
that occurred 19 (90.5%) women had an anal sphincter defect identified
with TPUS at delivery. No woman had an IAS injury that was diagnosed
clinically or with TPUS (Table 3). In addition, there were two (1%)
defects seen on ultrasound that were not clinically detectable. The
diagnostic performance of TPUS for detecting OASIs was evaluated, the
positive and negative predictive of TPUS being 91% and 99%
respectively (Table 4).
The relationship between the size of EAS defects identified clinically
and by ultrasound was also analysed. There was no correlation between
the grade of OASIs on clinical examination and on TPUS
(χ2 test, p=0.14) (Table 5).