Research In Progress
The incidence of double ovulation
Whilst dizgotic twinning rates are well characterised, it
is not known how many women will release two eggs during a
menstrual cycle instead of one. This number will obviously
be higher than the twinning rate since twins arise only if
both eggs successfully fertilise and develop. With our database
of ultrasound examinations we aim to determine the relative
number of those who ovulate one or two eggs in a non-pregnant
population. Correlation with the twinning rates may yield
interesting clues on human fertility, and may help explain
why rates of twinning vary so much between different racial
groups.
Prediction of IVF pregnancy success using
early ultrasound pregnancy markers
The corpus luteum (CL) is a vital hormone secreting structure
which forms on the ovary at the point spot where an egg is
released. It therefore reflects the number of eggs released
where the presence of one CL would mean that one egg has been
released.
The CL is a vital structure in early pregnancy since it is
known to secrete progesterone which nourishes and supports
early pregnancy. We have had an interest in investigating
whether the presence of a larger CL in early pregnancy may
protect the fetus and be associated with a lower risk of miscarriage.
Indeed, in a preliminary study of 235 cases there was a significantly
increased risk of miscarriage associated with a small CL measured
by ultrasound at 5-9 weeks of pregnancy. The miscarriage risk
was 5.9% for CL diameters at >90th centile (i.e. large
corpora lutea) and a 15.7% risk when the diameter was between
the 40-60th centile. If the CL diameter was <10th centile,
there was a 21.9% risk of miscarriage.
We believe that this sets the ground to be able to predict
the risk of miscarriage in women who had undergone a frozen
embryo transfer IVF cycle, and have a viable pregnancy demonstrated
at a 6 week ultrasound. Frozen embryo transfer cycles would
be expected to be mostly one corpus luteum present in the
ovaries unlike fresh embryo transfer where the medications
given initially produce multiple corpora lutea (treatment
cycle cysts).
Specifically, we would like to examine whether CL diameter
in association with, mean sac diameter-crown rump length,
can together provide a good estimation of miscarriage risk
in frozen embryo transfer cycle regimens in cases where there
is one corpus luteum present (e.g. some clomiphene citrate
cycles, or regimens where an embryo transfer is timed with
the women's natural cycle). We will also examine whether day
15-17 hCG levels also adds to risk estimation.
Investigating the outcomes of twins discordance
for size at 5-9 weeks gestation
Until recently, it was believed that the factors causing
low birthweight came into play during the middle of pregnancy.
Recently, several studies have pointed to factors occurring
earlier during pregnancy.
The significance of finding that one twin is smaller than
the other at ultrasound at 5-9 weeks is uncertain. It is a
dilemma for the clinicians since whether it heralds a poorer
outcome, which some suspect, is far from certain. We hypothesis
that in situations where one twin is found to be much smaller
than the co-twin as early as 5-9 weeks of pregnancy, there
will be an increased risk of low birthweight and chromosomal
abnormalities in the smaller twin.
We plan to investigate this hypothesis in an IVF cohort.
Should we show that this is the case, then the information
gained from this study will have direct implications on how
IVF clinicians counsel patients when faced with this ultrasound
finding.
Determining zygosity by early ultrasound
Recently, we have published a novel method to determine whether
twins are identical (monozygotic) or non-identical (dizygotic)
at an early pregnancy ultrasound by noting the number of corpora
lutea (CL), a structure which reflects ovulation (egg release).
In the presence of a dichorionic twin pregnancy (which can
be either monozygotic or dizygotic), the identification of
one CL would suggest that twins are monozygotic whereas two
CL's implies dizygosity. If need be, this could be further
correlated against chorionicity where, for instance, 2 CL's
(presumed Dz) and monochorionicity (certain Mz twins) would
suggest that the predicted zygosity is incorrect.
However, this clearly requires verification. We are in the
process of prospectively comparing ultrasound prediction of
zygosity at 5-9 weeks of gestation with DNA fingerprinting
of twins after delivery.
Low gestation sac and prediction of placenta
Praevia
This is a prospective study which sets out to establish the
range of distances of the gestation sac from the internal
cervical os in the first trimester and determine the relationship
between this measurement and the later development of placenta
praevia.
Third Trimester Doppler studies of the fetal
Middle Cerebral Artery
A prospective study which aims to establish the reference
range of the fetal middle cerebral artery blood flow in a
multiracial population and to compare this data with a population
of pregnancies complicated with symmetrical and asymmetrical
intrauterine growth retardation.
Size of the corpus luteum during the first trimester of pregnancy
We are collecting a large dataset characterising the size
of the corpus luteum at 5-13 weeks of gestation from over
1200 pregnancies. We aim to see whether it begins to regress
at the end of the 1st trimester when the fetus becomes less
dependent on its secretion of progesterone.
Intranasal (NET S21405 2575ug) and Endometrial
response
A multicentre collaborative trial which aims to determine
the effect on the endometrium of a new intranasal HRT preparation
NET S2140. Secondary evaluation criteria include presence
of endometrial hyperplasia after one year of treatment, vaginal
bleeding pattern, endometrial histology, general tolerance
and kinetic profile.
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