Diagnostic method for determining the susceptibility to delivery and reagent kit for use therefor

This application is a Continuation of U.S. application Ser. No. 11/048,685 filed on Jan. 31, 2005, which is a Continuation of co-pending application Ser. No. 08/360,815 filed on Dec. 29, 1994 and for which priority is claimed under 35 U.S.C. § 120. application Ser. No. 08/360,815 is the national phase of PCT International Application No. PCT/FI93/00275 filed on Jun. 29, 1993 under 35 U.S.C. § 371. The entire contents of each of the above-identified applications are hereby incorporated by reference. This application also claims priority of Application No. 923025 filed in FINLAND on Jun. 29, 1992 under 35 U.S.C. § 119.

The present invention relates to a diagnostic method for determining susceptibility to delivery based on a determination of a protein in a secretion sample taken from the vagina or the uterine cervix of a pregnant woman, and to a test kit designed for this purpose. Determination of susceptibility to delivery is particularly important in terms of the appropriate timing of induction of delivery when the pregnancy is post-term, or when a risk of preterm delivery is suspected.

Post-term pregnancies are a common yet difficult problem in connection with delivery. A pregnancy exceeding 41-42 weeks is considered post-term. Post-term pregnancies account for about 7-12% of all pregnancies, the duration of the pregnancy being calculated from the first day of the last menstrual period. About 4% of all pregnancies continue over 43 weeks. Diagnosis is difficult, even when the first day of the last menstrual period is known. Post-term pregnancy is associated with increased foetal and neonatal morbidity and mortality.

Perinatal mortality increases after the 42nd week of gestation, and doubles after the 43rd week.

Monitoring the well-being of the foetus is vital in cases of post-term pregnancy; delivery is, of course, immediately induced if there are any signs of foetal distress. If, on the other hand, the foetus is well, the next step is to decide the appropriate time for induction. It is generally accepted that labour should be induced as soon as the cervix is “mature” (shorter, softer and possibly partly dilated). Attempts to induce labour too early, i.e. when the cervix is not mature, lead to an increase in the number of sections. On the other hand, if the status of the foetus requires rapid delivery and it is known for sure that the cervix is not mature, the decision will be to operate right away.

The maturity of the cervix is usually determined using the so-called Bishop\'s score (Bishop E H, Obstet. Gynecol. 1964; 24: 266). The Bishop method involves assessing, by palpation, the size of the cervical orifice and the length, softness and direction of the cervical canal. The prior art method for determining the maturity of the cervix is not always sufficient for reliably predicting the time of delivery or for the timing of the induction of labour and estimating the likelihood of success.

Attempts to induce dilation of the cervix are not always successful. Prolonged labour increases the risk of maternal and foetal infection and the risk of foetal asphyxia, as well as being a psychologically unpleasant experience for the mother. Methods for more accurate assessment of the maturity of the cervix are therefore needed.

The present invention uses a completely new approach for predicting the time of delivery. The maturity of the cervix is assessed by determining the level of IGFBP-1, Insulin-like Growth Factor Binding Protein 1, produced by decidual cells, said assessment being performed on a vaginal or cervical secretion sample taken from a pregnant woman.

As the cervix matures and painless uterine contractions increase, the decidua, i.e. the endometrial lining of the mother\'s uterus and the chorion attached thereto start to become detached from each other in the lower segment of the uterus. When this happens, decidual cells become damaged and compounds synthesized by said cells are likely to “leak” from the cervix into the vagina.

The inventor of the present invention realized that a low but higher than a normal baseline IGFBP-1 concentration in a vaginal or cervical secretion is indicative of such “leakage” and is related to the maturation of the cervix and thus indicates an impending delivery. If no such maturation takes place in the lower segment of the uterus, the chorion remains attached to the decidua and no decidual cell product is found in said secretion.

Determination of IGFBP-1 can therefore function as a biochemical test for assessing the maturity of the cervix and thus the time of delivery, or for deciding when induction should be started. Said test can also be used to identify women in whom induction probably would not help to dilate the cervix, thus helping to prevent prolonged induction attempts, with the attendant risks to both foetus and mother.

Another situation where a correct estimate of the time of delivery is critical, is when a preterm delivery is suspected. Predicting a preterm delivery is difficult. Identification of the risk factors involved helps to predict only a very small proportion of preterm deliveries.

Predicting a preterm delivery on the basis of uterine con-tractions is often difficult. Preterm contractions may be so weak that neither the woman nor the attendant nurse or physician will notice them. On the other hand, out of the women who feel preterm contractions and whose contractions are also objectively verifiable, only about 10-20% are believed to need treatment to prevent a possibly impending preterm delivery. It is difficult to identify these 10-20%. However, in order to minimize the number of preterm deliveries, it would be important to be able to identify such patients as early as possible, i.e. as soon as contractions start appearing.

Patients having any of the risk factors indicative of preterm labour should be especially closely monitored. In ideal cases, after a positive result in a test predicting preterm labour, a preterm delivery could be better prevented by medication and changes in lifestyle. Diagnosed preterm rupture of foetal membranes and vaginal bleeding are as such signs of impending preterm labour, and laboratory tests are not needed in such cases. However, if the foetal membranes are intact, only regular contractions and observed changes in the cervical canal (shortening of the canal and opening of the orifice to 2 cm or more) are generally considered diagnostic criteria for an impending preterm delivery and indications for hospital admission. This may, in certain cases, prove to be too late.

Several scoring systems have been developed for predicting the risk of preterm labour. The scores are calculated during the first pregnancy examination and used later for purposes of comparison. However, these prior art systems only help to chart about half of the pregnancies that end in preterm delivery. On the other hand, based on said scoring systems, many women who do not deliver their babies preterm end up in the risk group. Attempts have been made to devise biochemical

tests (e.g. determination of blood oestradiol, blood progesterone and prostaglandin levels) but with poor results.

The methods used so far have not provided a reliable basis for predicting the significance of preterm contractions and thus the likelihood of preterm labour. Therefore, it has not been possible to direct prophylactic treatment at the right group of pregnant women. In some women, preterm contractions are so weak that they remain unnoticed until the labour is so advanced and the cervix so dilated that the foetal membranes rupture. The only choice is to treat those women who already have clinically observable contractions. However, only in certain cases do preterm contractions lead to preterm labour, and thus only this portion of the women who have clinically confirmed preterm contractions need prophylactic treatment (rest and tocolytic agents, i.e. agents inhibiting uterine contractions). On the other hand, it has been found that tocolytic treatment is ineffective and that preterm labour cannot be prevented if considerable changes have already taken place in the cervix before the medication is started.

The method according to the present invention, wherein the amount of IGFBP-1 in a vaginal or cervical secretion sample is determined, can be used in the prediction of preterm labour.

The protein IGFBP-1 is a product of the decidual cells. It is found in the vaginal secretion of non-pregnant women only during menstruation. Urine and seminal plasma, which may be present in the vagina of pregnant women, contain only very low concentrations of IGFBP-1.

The inventor of the present invention, Eeva-Marja Rutanen, has previously shown that rupture of the foetal membranes can be confirmed by determining the IGFBP-1 concentration in a vaginal secretion. International Patent Application PCT/FI91/00413 is based on said observation. It was also shown that vaginal secretion may contain small amounts of IGFBP-1 even if the foetal membranes are intact.

It can generally be assumed that biological membranes such as foetal membranes may allow the passage of small amounts of compounds and leak fluids such as amniotic fluid into the vagina even if the membranes are intact. This would result in steady or occasional low concentrations of IGFBP-1 in the vaginal or cervical secretion. The inventor of the present invention realized that a rising but low IGFBP-1 level does not represent the baseline level that would result from amniotic fluid leaking through intact membranes. The IGFBP-1 present in the secretion is not a result of ruptured membranes either, since its level is low; instead it originates from decidual cells in which some change is taking place. This change is the detachment of foetal membranes from each other which occurs before labour.