More precise due dates for average pregnancy?
To the frustration of busy pregnant women everywhere, the estimate of when she'll actually give birth can be off by as much as two to three weeks — early or late. Now, a routine screening could help narrow the estimated date of delivery to seven days from the time of the test.
Women often have a window of more than a month in which carefully laid plans can be thrown into disarray. Only 5 percent of women deliver exactly on their due date. A new meta-analysis suggests that one routine screening test could help mothers narrow that window to seven days from the time of her test.
research was published October 28th in BJOG: An International Journal of Obstetrics and Gynaecology.
"Measuring cervical length via ultrasound at around 37-39 weeks can give us a better sense of whether a mother will deliver soon — or not."
Vincenzo Berghella MD, Director of Maternal Fetal Medicine at Thomas Jefferson University Hospital, Professor of Obstetrics and Gynecology, Sidney Kimmel Medical College at Thomas Jefferson University and senior author.
Until now, measuring cervical length has been used to help detect women with a high chance of premature labor - the shorter the cervix, the more likely labor is imminent.
Since the method is considered the gold standard for detecting preterm birth, a number of researchers have investigated whether it could be used to help predict birth at term as well. The results have produced debate in the field, with some studies showing poor predictive value, others showing stronger value. Dr. Berghella and colleagues' aim was to pool the data from comparable studies using transvaginal ultrasound to test cervical length, and come to a consensus.
Researchers pooled data from five prospective studies. These included 735 women with single-child pregnancies in the proper head-down position.
Researchers found that when the cervix measured more than 30 millimeters at a woman's due date, she had less than a 50 percent chance of delivering within seven days.
However, when the cervix measures 10 mm or less, a woman had more than an 85 percent chance of delivering within seven days.
Cervical length is a good predictor because it tracks the natural progress of a woman's body toward labor.
When a woman's body prepares for labor, a number of changes start to take place. The cervix, which has kept the baby from descending down the birth canal for the nine months of pregnancy, begins to soften. It changes its usual "ice cream cone" shape — when an ice cream cone is held upright — to a shorter cone with a flattened top pressing against the curve of the uterus.
When the process begins too early, it signals a preterm birth, which caught in time can be delayed with medications.
"Women always ask for a better sense of their delivery date in order to help them prepare for work leave, or to make contingency plans for sibling-care during labor. These are plans which help reduce a woman's anxiety about the onset of labor.
"But having a better sense can also help obstetricians provide information that could help improve or even save a mother or baby's life. For example, women with a higher risk of stillbirth may be better off receiving labor induction. If the cervix is still long at her due date, the chances of timely spontaneous birth are low."
The possibility to predict the delivery date is a question frequently raised by pregnant women. However, a clinician has currently little to predict when a woman at term will deliver.
To evaluate the predictive accuracy of transvaginal ultrasound (TVU) cervical length (CL) for spontaneous onset of labour in singleton gestation enrolled at term by a meta-analysis.
We performed a literature search in electronic databases.
We included only studies assessing the accuracy of TVU CL in prediction of spontaneous onset of labour in singleton gestations with vertex presentation who were enrolled at term.
Data collection and analysis
The primary outcome was the accuracy of CL for prediction of spontaneous labour within 7 days. Pooled sensitivities and specificities were calculated.
Five studies including 735 singleton gestations were included. For the prediction of spontaneous labour within 7 days for CL <30 mm the pooled sensitivity was 64% and pooled specificity was 60%. The higher the CL, the better the sensitivity; the lower the CL, the better the specificity. A woman with a singleton gestation at term and a TVU CL of 30 mm has a <50% chance of delivering within 7 days, while one with a TVU CL of 10 mm has an over 85% chance of delivery within 7 days.
TVU CL at term has moderate value in predicting the onset of spontaneous labour. A woman with a TVU CL of 10 mm or less has a high chance of delivering within a week.
The authors report no conflicts of interest.
Article Reference: G. Saccone et al., "Transvaginal ultrasound cervical length for prediction of spontaneous labor at term: a systematic review and meta-analysis," BJOG, DOI: 10.1111/1471-0528.13724, 2015.
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