Category Archives: Preterm Birth

Preterm Birth

A New FDA-Approved Test for Predicting Preterm Delivery


Preterm baby

According to the March of Dimes, preterm birth occurs in approximately 10% of U.S. pregnancies. Until recently, cervicovaginal fetal fibronectin (fFN) was the only FDA-approved test for predicting preterm delivery in symptomatic women. We have blogged about fFN previously

Despite its FDA approval, fFN has limited clinical value. A condition with low prevalence, such as preterm delivery, has a low pre-test probability of occurring, hence a negative test result adds little to the assessment of the patient. Thus, a screening test for a low prevalence condition must demonstrate high positive predictive value (PPV) to be useful. The negative predictive value (NPV) of fFN is 99.5%, meaning a negative result is highly predictive that a woman will NOT deliver soon. However, PPV of fFN is only ~17%, meaning that less than 1 in 5 women with a positive test result will proceed to delivery with 7-14 days. For comparison, the PPV of flipping a coin in this population is 4%. Meta-analyses have supported the lack of utility for fFN.

In April 2018, the FDA approved cervicovaginal placental alpha macroglobulin-1 (PAMG-1), (brand name Parto Sure from QIAGEN) as a test for assessing the risk of spontaneous preterm birth in patients with symptoms of preterm labor.

Several recent studies have evaluated PAMG-1 for its ability to predict preterm birth.

Wing, et al. conducted a prospective study of pregnant women from 15 US sites, with signs or symptoms of preterm labor between 24 and 35 weeks of gestation with intact membranes and cervical dilations less than 3cm (>3 cm generally indicates active labor). They compared the utility of PAMG-1 to fFN. A summary of their key findings are shown in the table below.

Spontaneous preterm delivery ≤ 7 days

PPV

NPV

PAMG-1

19.0%

99.1%

fFN

6.5%

99.7%

     

Spontaneous preterm delivery ≤ 14 days

   

PAMG-1

25.0%

97.7%

fFN

11.1%

98.7%

Cervicovaginal PAMG-1 demonstrated similar negative predictive value and improved positive predictive value compared to cervicovaginal fFN.

Similarly, Melchor, et al. conducted a retrospective study of women with preterm contractions presenting to a single maternity hospital in Spain. They compared a one year period during which fFN was used to assess risk of pre-term delivery and a one year period where PAMG-1 was used. Similar to the Melchor study, patients were between 24-34 weeks of gestation with signs or symptoms of preterm labor and had intact membranes and a cervical dilation less than 3cm. A summary of their key findings are shown in the table below.

Spontaneous preterm delivery ≤ 7 days

PPV

NPV

PAMG-1

35.3%

98.3%

fFN

7.9%

97.9%

Both studies show improved positive predictive values for PAMG-1 over fFN. However, both studies reported sensitivities for PAMG-1 of 50%.  While this test can certainly be viewed as an improvement over fFN, PAMG-1 will only identify half of the women who will deliver within 7 day. Clearly a better marker to predict pre-term delivery is still needed.

Can a personalized approach improve IVF success rates?


Test Tube Baby

This post was written by Robert D. Nerenz, PhD, an assistant professor of pathology and laboratory medicine at the University of Kentucky, in Lexington.

In the United States, an estimated one in seven couples experience infertility and for many of these couples, in vitro fertilization (IVF) represents their best chance of achieving pregnancy. However, IVF cycles constitute a significant expense (approximately $12,500 per cycle), disrupt patients’ daily lives and only result in a healthy, live birth 30% of the time! Furthermore, the majority of IVF cycles performed in the United States involve the transfer of multiple embryos. This is of particular concern because multiple embryo transfer carries a finite risk of a multiple gestation pregnancy. Bringing multiple infants to term is associated with an increased risk of poor fetal and maternal outcomes including decreased birth weight, increased rate of fetal death, preeclampsia, gestational diabetes and preterm labor. Clearly, there is a significant need to improve IVF success rates while also minimizing the likelihood of multiple gestation pregnancies.

One strategy that may accomplish both of these goals is to perform “single embryo transfer” by implanting one embryo that has a high likelihood of producing pregnancy and, ultimately, a live birth. This is the focus of an upcoming symposium at the AACC meeting to be held July 29th at 10:30 am in Atlanta, Georgia. Fertility clinics around the world currently attempt to do this by observing embryos under a microscope and choosing the best embryo on the basis of its physical appearance. Unfortunately, this approach does not provide any information about the embryo’s genetic status. This is an important limitation because aneuploidy (the gain or loss of a chromosome) is the most common cause of pregnancy loss. It is also estimated to occur in ≥10% of clinical pregnancies and becomes more frequent with increasing maternal age.

To ensure that aneuploid embryos are not selected for transfer, several research groups have developed methods collectively known as comprehensive chromosome screening (CCS). CCS involves culturing embryos for 5-6 days, removing a few cells from the trophectoderm (the outer cell layer that develops into the placenta), isolating the DNA from those cells and assessing the copy number of each chromosome using techniques such as quantitative PCR, comparative genomic hybridization, or single nucleotide polymorphism arrays. Following determination of the embryos’ genetic status, only embryos with the normal number of chromosomes are chosen for transfer. In multiple prospective, randomized controlled trials described here and here, CCS has been shown to increase the pregnancy rate and decrease the frequency of multiple gestation pregnancies. As a result, CCS is beginning to make the transition from the research setting to use with patients.

The ability to transfer only euploid embryos represents the most promising application of novel technologies to IVF but ongoing research is focused on other ways to improve the IVF success rate. Many different groups are analyzing the culture medium that embryos are grown in prior to implantation. It is hoped that this will provide information about the embryos’ metabolic health and might help identify which embryos are most likely to result in pregnancy and live birth. Other groups are evaluating endometrial gene expression profiles to assess endometrial receptivity and ultimately determine the best time to perform embryo transfer. While both of these approaches have technical limitations and are not quite ready for primetime, they have the potential to greatly improve our current standard of care and may be ready for clinical use in the near future.

Laboratory testing for premature rupture of membranes


This post is by a guest author, Douglas Stickle, Ph.D.  Dr. Stickle is a professor in the Department of Pathology at Thomas Jefferson University and the director of chemistry and point-of-care testing at Jefferson University Hospitals in Philadelphia, PA.

Rupture of membranes (ROM) is the term used to describe the breaking of the amniotic sac, as normally occurs before the onset of labor. If this happens earlier than the 37th week of pregnancy it is called preterm ROM (PROM). It’s a condition that can lead to a preterm birth, or, if very early, a preterm, premature birth.

Preterm baby 2When PROM happens, there is an increased risk of complications due to intrauterine infection, umbilical cord compression, and the neurodevelopmental disorders that are associated with a preterm delivery. Diagnosis of PROM is particularly important when the gestational age is incompatible with a viable birth, often considered to be a fetal age less than 24 weeks. In such cases, medical intervention is necessary to preserve the chances for a live birth.

Suspected cases of PROM are often investigated by laboratory analysis of fluid obtained from the vagina to detect properties or substances that should otherwise not be present unless the fluid contains amniotic fluid due to PROM. The simplest forms of testing are measurement of acidity (pH) of the fluid, or a test called "fern" testing. Fern testing refers to the fern-like appearance of amniotic fluid when it is dried on a glass slide. Both of these tests aren’t very accurate and so other tests have been developed to better identify patients with ruptured membranes.

These other tests are designed to detect molecules that are normally present in amniotic fluid but not vaginal fluid. For example, tests have been developed that detect alpha-fetoprotein (AFP) or insulin-like growth factor binding protein-1 (IGFBP-1). The presence or absence of these molecules in the specimen are determined by a lateral flow immunoassay. The assay works like commonly performed tests for human chorionic gonadotropin (hCG) (aka pregnancy tests).

These tests are highly sensitive to low concentrations of these molecules, which is both good and bad. It’s good because they can detect small amounts of the molecules and lead to a more accurate diagnosis. It’s bad because these two molecules are also present in maternal blood which means that if a sample is contaminated with blood, the certainty of a positive test to detect amniotic fluid is called into question.

From the doctor’s perspective, a practical advantage of the immunoassays is that their results are binary – the result is either positive or negative — whereas the pH test and the fern test are more subjective and difficult to interpret definitively. However, the AFP and IGFBP-1 tests may be subject to false-positive results as the gestational age of the fetus approaches term. This suggests that, at later stages of pregnancy, these biomarkers may signify imminence of delivery.

The gold standard, or best test, to diagnose rupture of membranes is a dye test, in which a colored fluid is injected into the amniotic fluid followed by direct observation to see if the dye subsequently appears in the vaginal pool fluid. Also, ultrasound imaging of the amniotic fluid volume may also assist in diagnosis of PROM, but in individual cases such imaging may be difficult to interpret. Given the low but finite risk of complications of the dye test, the AFP and IGFBP-1 tests are often preferred as first-line tests for preterm premature rupture of membranes.

Predicting preterm birth


Preterm baby Preterm birth is a serious problem. Defined as delivery before 37 completed weeks, infants born preterm are at high risk of complications such as respiratory distress syndrome, bleeding into the brain, poor neurological development, and cognitive impairment. Further, preterm birth is responsible for ~75% of death in newborns without genetic anomalies.

Unfortunately, the vast majority of treatments provided to pregnant women with symptoms of preterm labor have done little to prevent preterm birth. About 13% of pregnancies end with preterm delivery and this percentage has increased steadily over the last few decades.

Risk factors for preterm birth include mother's age, socioeconomic status, and being pregnant with more than one fetus. A woman who has had a previous preterm delivery is also at risk of delivering subsequent pregnancies early as well. Preterm birth is also more common among black women compared to other ethnic groups which appears to be unrelated to socioeconomic status or other factors.

Symptoms of preterm labor are just like symptoms of term labor. However, early contractions occur frequently in pregnant women and don't always mean they are in actual preterm labor. In fact, most women with early symptoms go on to delivery term babies. This makes it difficult to diagnose true preterm labor when it occurs. A test that could accurately predict preterm labor would be helpful.

Currently there is only one lab test approved for use to predict preterm labor. Fetal fibronectin (fFN) is a protein produced by the fetal membranes during pregnancy. Although it can be detected in cervicovaginal fluid early in pregnancy it usually becomes undetectable between weeks 25 and 35. After that, it becomes detectable again after 37 weeks. In women with preterm labor, fFN can be detected in cervicovaginal fluid during the time that it is usually not present. This may occur because of a break down of the fetal membranes or in response to inflammation.

A recent study compared the ability of fFN and a interleukin-6 (IL-6), an inflammatory cytokine, to predict preterm birth. The tests were performed in 667 samples collected from 580 women with and without symptoms of preterm labor. About half of the women in the study were black.

In both groups, a positive fFN result was significantly associated with preterm birth occurring within 14 days of testing. However, the actual likelihood of delivery early was still rather low. Like other studies, this one also showed that the strength of the fFN test is it's negative predictive value. That is, the absence of fFN is a much stronger indicator that preterm birth won't occur.

IL-6 was also significantly associated with preterm birth but only in the black women. Like fFN, it also wasn't a strong predictor in this population but it was much better than fFN in either the black or non-black groups.

There's still much to learn. We don't really understand the different processes (which are multifactorial) that lead to preterm delivery. Also, it's clear that the events that lead to preterm delivery are probably not the same between women of different ethnic backgrounds. As such, a single predictor of preterm delivery is probably not going to work well. Combination testing, such as fFN and IL-6 (or other, yet to be discovered markers) may yield more promising results than any one marker alone.