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Gynecological Endocrinology, 2013; 29(2): 129–132© 2013 Informa UK, Ltd.ISSN 0951-3590 print/ISSN 1473-0766 onlineDOI: 10.3109/09513590.2012.730574

Background: Insulin-like growth factor (IGF) binding protein-1 (IGFBP-1) is the main binder of IGFs in secretory endometrium and decidualized stromal endometrial cells and IGFBP-1 has been shown to modulate IGF bioactivities and influ-ence fetal growth. To be able to evaluate IGFBP-1 values during pregnancy it is important to establish normal values in pregnant women. Materials & Methods: We have studied IGFBP-1 concentrations in maternal plasma from 52 healthy women with normal singleton pregnancies. Several plasma samples were collected from each woman and the samples were grouped according to gestational age into the following periods: week 7–17; week 17–24; week 24–28; week 28–31; week 31–34; week 34–38; −2 to 0 weeks prior to delivery and postpartum (>6 weeks after delivery). Results: The 2.5 and 97.5 percentiles for IGFBP-1 were calculated according to the recommendations of the International Federation of Clinical Chemistry on the statistical treatment of reference values. Conclusions: IGFBP-1 is increased during pregnancy compared to postpartum. Two peaks, at week 17–24 and just before delivery, were observed.

Keywords: IGFBP-1, human, pregnancy

IntroductionInsulin-like growth factor-binding protein 1 (IGFBP-1), also known as placental protein 12 (PP12) [1], is a member of the insulin-like growth factor-binding protein (IGFBP) family. All members of the IGFBP superfamily are cysteine-rich [2]. The protein family consists of six high-affinity insulin-like growth factors (IGFs) binding proteins and several low-affinity binding proteins referred to as IGFBP related proteins. IGFBP is involved in the regulation of IGF I and II and modulates the half-life of these IGFs [3] and have been shown to either inhibit or stimulate the growth promoting effects of IGF I and II [4]. Growth hormone (GH) is secreted by the anterior pituitary gland under the control of hypothalamic factor GH Releasing Hormone. GH acts through insulin-like growth factor-1 (IGF 1).

IGFBP-1 is the predominant IGF binding protein in secre-tory endometrium and decidualized stromal endometrial cells [5]. In the ovaries, IGFBP-1 may influence ovulation, follicular

growth and steroidogenesis [6,7]. IGFBP-1 is also believed to be of importance for differentiation, proliferation and decidu-alization of the endometrium as well as trophoblast invasion, implantation and fetal growth [8,9]. High levels of IGFBP-1 may lead to poor implantation and subsequent miscarriage [10]. In humans, trophoblast invasion has a key role for the widening of the spiral arteries [11]. If this invasion fails, preeclampsia and/or intrauterine growth retardation (IUGR) might follow. Transgenic animals over- expressing IGFBP-1 show poor fertility and high concentrations of IGFBP-1 may lead to reduced fetal growth [12,13]. IGFBP-1 has been shown to be increased in patients with pre-eclampsia [8,14]. Increased placental gene expression as well as protein levels of IGFBP-1 has been shown to be associated with IUGR [15–17] and cord blood levels of IGFBP-1 has been shown to correlate with reduced fetal growth [18]. On the other hand, decreased placental expression of IGFBP-1 has also been reported to be associated with fetal growth restriction [19] and decreased serum levels of IGFBP-1 has been reported to be a prognostic marker for pre-eclampsia [20,21].

To be able to interpret levels of IGFBP-1 during complicated pregnancy it is important to have values from normal pregnancies for comparison. The aim of this study was to investigate maternal plasma levels of IGFBP-1 in longitudinally collected samples throughout pregnancy and postpartum from healthy women with normal pregnancies.

Materials and methodsInclusion criteria were healthy women at least 18 years old with a normal, singleton, spontaneous pregnancy. Exclusion criteria were non-Swedish speaking women and women taking drugs other than iron or folic acid. At the antenatal clinic the pregnant women were given written and verbal information about the study by the midwife and all participating women gave their consent. A total of 59 women were recruited consecutively but seven were withdrawn from the study; four due to miscarriage, one moved from the county and two did not continue the study. Fifty-two women with normal pregnancies completed the study and were included in the reference material (Table I). All women attended routine antenatal care and blood samples were taken throughout pregnancy and postpartum after overnight fasting. The aim was to collect samples around gestational weeks 12,

Gestational diabetes

Insulin-like growth factor binding protein-1 (IGFBP-1) during normal pregnancy

anders larsson1, Maria Palm2, samar basu3,4 & ove axelsson2,5

1Department of Medical Sciences, Clinical Chemistry, Uppsala University, Uppsala, Sweden, 2Department of Women’s and Children’s Health, Obstetrics and Gynecology, Uppsala University, Uppsala, Sweden, 3Department of Public Health and Caring Sciences, Oxidative Stress and Inflammation, Uppsala University, Uppsala, Sweden, 4Laboratoire de Biochimie, Biologie Moléculaire et Nutrition, Faculté de Pharmacie, Université d’Auvergne, Clermont-Ferrand, and EA4233 Nutrition, Cancérogenese et Thérapie Anti-tumorale, UFR Pharmacie, CLARA, CRNH-A, Clermont-Ferrand, France, and 5Clinical Research Centre, Sörmland, Uppsala University, Uppsala, Sweden

Correspondence: Anders Larsson, Department of Medical Sciences, University Hospital, S-751 85 Uppsala, Sweden. Tel: 46-18-6114271. Fax: 46-18-552562. E-mail: anders.larsson@akademiska.se

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20, 24, 28, 32, 36, 40, during parturition as well as 6 weeks or more after delivery (Table II). Plasma samples were collected in gel tubes with lithium-heparin (LH PST™ II, BD Vacutainer Systems, Plymouth, UK) after an overnight fast. Gestational age was estimated through an ultrasound scan in the second trimester and presented as completed weeks. The study was approved by the local Ethical Board at Uppsala University.

The analyses were performed without knowledge of the patient data. Samples were analysed using a commercially available ELISA kit for IGFBP-1 (DY871, R&D Systems, Minneapolis, MN, USA). Briefly, the microtitre plates had been coated with monoclonal antibodies specific for IGFBP-1 and the first step was to add stan-dards and samples to the wells. During the following incubation period IGFBP-1 present in standards and samples was bound to the immobilized antibody. After a thorough wash a biotinylated antibody specific for IGFBP-1 was pipetted into the wells. After incubation with the biotinylated antibodies and washing a strep-tavidine-HRP conjugate was added and following an additional incubation-and wash step a substrate solution was added and color developed in proportion to the amount of IGFBP-1 bound. The color development was subsequently stopped and the inten-sity of color was measured by photospectrometry. Calculation of results was performed according to manufacturer’s recommen-dations. The assays had a total coefficient of variation (CV) of approximately 7%.

Statistical analysis

Calculations of reference intervals were performed by boot-strap estimation utilizing RefVal 4.0 (Department of Clinical Chemistry, Rikshospitalet, N-0027 Oslo, Norway). RefVal fulfils the recommendations of the International Federation of Clinical Chemistry on the statistical treatment of reference values [22,23]. Difference between sampling periods was tested with Mann–Whitney (Statistica 7.1, Statsoft, Tulsa, Okla, USA).

ResultsCharacteristics of the women and their newborn infants are described in Table I. All pregnancies were singleton and all deliv-eries took place at Uppsala University Hospital 2004–2005. The sampling periods and the number of samples are presented in Table II.

The lowest IGFBP-1 values were observed in the postpartum samples (median value 23797 pg/mL) (Figure 1). IGFBP-1 exhib-ited two peaks during pregnancy, one at week 17–24 and the other before delivery with a plateau between the two peaks. All pregnancy periods showed significantly higher values than the postpartum values (p < 0.0001 for all studied periods). The levels at week 7–17 were significantly higher than the postpartum levels, although significantly lower compared to all other pregnancy periods (p < 0.02 for all periods).

The 2.5 and 97.5 percentiles for each time period are presented in Table III and Figure 1.

DiscussionIn this population study of healthy women, with uncompli-cated singleton pregnancies, IGFBP-1 was significantly elevated throughout pregnancy in comparison with the postpartum period. There were two peaks in IGFBP-1 concentrations, one at week 17–24 and the other just before delivery. There are a number of longitudinal studies of IGFBP-1 during pregnancy. The sampling periods vary which makes it a bit difficult to make direct comparisons. For instance Olausson et al. [24] reports a gradual increase in IGFBP-1 up to delivery in contrast to our finding of an initial peak around week 17–24. However, if we look at the longitudinal curves for IGFBP-1 of individual women a number of the study subjects had a clear IGFBP-1 peak around week 14 although it is less pronounced in comparison to our study. Clapp et al. [25] also reports slightly higher IGFBP-1 values at week 16 in comparison with week 24 and 32. Skjaerbaek et al. [26] did not report a finding of an early IGFBP-1 peak. Three of the studies show individuals with an IGFBP-1 peak in the beginning of the

Table I. Characteristics of the women (n = 52) and their newborn infants. Characteristics n = 52 n (%) Mean (SD)Maternal age (years) 52 32 (4)BMI (at booking) 51 24 (4)Primipara 28 (53.8)Way of delivery Vaginal 43 (82.7) Caesarian section 9 (17.3)Ceaserean section Elective 3 (5.8) Emergency 6 (11.5)Vaginal induction 6 (11.5)Gestational age at delivery (Days) 52 280 (13)Infant gender Female 22 (42.3) Male 30 (57.7)Birthweight at delivery (grams) 52 3524 (571)Apgar ≤ 7 at 5 min 0All pregnancies were singleton and all deliveries took place at Uppsala University

Hospital, Sweden. The characteristics are given as mean values and standard devia-tions (within brackets).

Table II. Description of the different sampling periods.

Gestational weeks Sample sizeMedian time in

weeks Range in weeks7–17 50 11.1 7.5–16.017–24 51 20.6 18.5–23.324–28 49 25.7 24.0–28.028–31 46 29.1 28.1–30.931–34 47 32.3 31.1–33.934–38 52 36.0 34.0–37.9Predeliverya 43 −2 days −14 to 0 daysPostpartuma 51 72 days 45–202 daysaThe time presented for the predelivery group is the number of days before delivery

and for the postpartum group the number of days after delivery.

Figure 1. Median and interquartile range for IGFBP-1 during different stages of pregnancies and postpartum.

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second trimester indicating that there are females with an early increase. Further studies are warranted to explore the role of this increase.

Low levels of IGFBP-1 in the first trimester have been reported in women who later developed preeclampsia [20,21]. The exact mechanism behind the association between low levels of IGFBP-1 and preeclampsia is not clearly established. It may be due to impaired placental perfusion, but it may also be due to impaired glucose tolerance and increased insulin resistance. A seemingly contradictory finding that women with low IGFBP-1 throughout pregnancy delivered infants with relatively higher birth weight [27] was recently published. Such results are however in line with Akram et al. [28], who found higher levels of placental IGFBP-1 in small for gestational age (SGA) pregnancies and Guidice et al. who reported higher circulating levels of IGFBP-1 in preeclampsia [29]. The proposed mechanism was decrease of free IGF [30]. In contrast, Koutsaki et al. showed that decreased placental expres-sion of IGFBP-1 was associated with fetal growth restrictions [19]. So, it seems to be discrepancies between the studies regarding the effects of IGFBP-1 on fetal development and the development of pre-eclampsia. However, similar findings have been described for other placental proteins [20,21].

Phosphorylated IGFBP-1 is produced by the uterine decidua and the concentration of phosphorylated IGFBP-1 has been used as a marker for preterm labor [31]. IGFBP-1 thus seems to have several important roles during pregnancy from implantation to delivery. To be able to evaluate laboratory test results from pregnant women with suspected pregnancy complications, it is important to have appropriate reference values from normal pregnancies.

This study reports plasma values of IGFBP-1 throughout normal pregnancy and postpartum. These reference values are important when evaluating IGFBP-1 results from pregnant women.

Declaration of Interest: This study was financially supported by the Uppsala University Hospital Research Fund, Gillbergska foundation, the research fund for the Uppsala-Örebro region and the research fund for the county of Sörmland.

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Table III. Calculated lower (2.5 percentile) and upper (97.5 percentile) limits for the reference interval and 90% confidence intervals (in brackets) for IGFBP-1 during different stages of pregnancies and postpartum. Gestational weeks Lower limits Upper limitIGFBP-1 pg/mL Week 7–17 19973 (14892–25054) −188791 (171073–206509) Week 17–24 34069 (25250–42888) −294922 (282708–307136) Week 24–28 15226 (−9259–39710) −356575 (263608–449541) Week 28–31 35309 (30496–40122) −259223 (221021–297425) Week 31–34 24239 (5946–42532) −305447 (221054–389840) Week 34–38 15574 (−3359 to 34507) −304661 (263211–346111) Predelivery 8948 (−9964 to 27860) −374537 (304783–444292) Postpartum 2601 (474–4727) −158022 (134917–181126)

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