Methods
This was a prospective observational study of women attending the Early
Pregnancy Assessment Unit at University College London Hospital between
April 2017 and March 2019. Only clinically stable women who presented
with mild to moderate vaginal bleeding and/or pelvic pain were included
into the study. They were all seen by a single operator (E.B) who had
extensive experience in scanning of women with endometriosis in a
tertiary Endometriosis Centre. A single operator was used in order to
reduce the inter-observer variability associated with ultrasound
diagnosis of endometriosis. We recorded women’s demographic data,
indications for attendance and a detailed medical history. This included
their age, ethnicity, body mass index (kg/m2), smoking
status, gravidity and parity. All pregnant women that had a transvaginal
ultrasound scan were included in the study. All scans were performed in
a standard fashion using a 7.5-Mhz probe (Voluson E8, GE Medical
Systems, Milwaukee, WI, USA). The uterus was examined for the presence
of congenital uterine anomalies, adenomyosis and fibroids. Congenital
uterine anomalies were described using the revised ASRM
classification.17 The diagnosis of adenomyosis and
fibroids was made in accordance with previously described diagnostic
criteria.13,18 The ovaries and adnexae were then
examined. Women were considered to have a diagnosis of endometriosis if
there was evidence of endometriotic ovarian cysts and/or deep
endometriotic nodules. Ovarian endometriomas were defined as
thick-walled and well circumscribed cysts with low-level internal echoes
(‘ground glass’).19 Endometriotic nodules present as
hypoechoic or isoechogenic solid lesions with irregular borders that
were fixed to surrounding pelvic structures.10,20Statistical analysis was performed to establish the prevalence of
endometriosis in addition to possible associations between demographic
and clinical variables using logistic regression and multivariate
analysis. Analysis was performed using SPSS software (SPSS Inc.,
Chicago, IL, USA). All clinical findings were stored in a clinical
database that facilitated data entry and retrieval (PIA‐Fetal Database,
Viewpoint Bildverabeitung GmbH, Wessling, Germany). The study was
registered on Research Registry (Unique identifying number:
researchregistry4569). A retrospective audit of records of 750 women who
attended our unit during the first trimester of pregnancy (4-14 weeks’
gestation), showed a 3.2% prevalence of ovarian and deep endometriosis.
Based on this information we calculated that the required sample size
for our study was 1176 to achieve a precision of 1% with 95%
confidence interval.