Three-dimensional ultrasound of the cervix during midpregnancy screening ultrasound

Preterm delivery is major health issue and is one of the main reasons of
perinatal mortality. The incidence is about 5 * 8 % and seems to be rising in
developed countries. This all is a burden on general health care. Previous
research showed that a shortened cervical length in late second trimester or
early third trimester is related to a higher risk on preterm delivery. The
earlier the shortened cervical length and the shorter the cervical length, the
higher the risk. The cervical length is measured by a two-dimensional
trans-vaginal ultrasound. Due to anatomical features of the cervix and
limitation by a two-dimensional view, the length measured by a two-dimensional
is not perfect and measuring errors do occur. This results in both over and
under-estimation of the cervical length. A recent review reports that
two-dimensional ultrasound of the cervix is not applicable as a screening
instrument.
Untill now, there is no evidenced based protocol for risk management in case of
a shortened cervical length. In the Netherlands, this is a research topic in
the national TRIPLE P consortium study.
Several years ago, three dimensional ultrasound was introduced. Since
introduction of this technique, measuring of a volume is possible. Great
advantage of this three-dimensional technique is the additional coronal view

The most recent report on three dimensional measured cervical volume date from
2006, using imaging dating from 2004.
Measuring cervical volume is promising due to the assumption that small
alterations in cervical length result in bigger changes in cervical volume.
Until recently, three dimensional had is technical limitations due to little
contrast between cervix and surrounding tissues. Research showed variable
results in diagnostic power of three dimensional ultrasound. These limitations
are most likely discarded by technical improvement, allowing a better risk
assessment. This, combined with more and better treatment options hopefully
leads to a drop in the incidence of perinatal mortality.

-Comparing two-dimensional and three-dimensional ultrasound length measurement
-Evaluate improvement in three dimensional ultrasound imaging. Assessing
possibility of cervical volume measuring.
-Assessing intra- and inter-observer variation of cervical volume measruments
-Assessing average value of cervical volume at 18-20 weeks of ammenorrhoea

Prospective cohort study

The patients will be included after informed consent for both transvaginal
ultrasound and data collection about pregnancy outcome. No questionnairs will
be used.

Extensive medical research has shown that there are no risk of negative
side-effects of ultrasound on pregnant women and the unborn child.

The extra-burden for the patients consist of, additional to a abdominal
ultrasound, a transvaginal ultrasound. This additional ultrasound will cost an
extra 5 minutes. Pain is very rare during transvaginal ultrasound.

The patient will have no direct substantial benefit from participating in this
study. Benefit will consist of better diagnostic tools in the future.