Do placentae of term singleton pregnancies obtained by assisted reproductive technologies differ from those of spontaneously conceived pregnancies?

Y. Daniel1, L. Schreiber3, E. Geva2, A. Amit2, D. Pausner1, M.J. Kupferminc1 and J.B. Lessing1,4

1 Department of Obstetrics and Gynecology, 2 The Sara Racine IVF Unit, Lis Maternity Hospital, and 3 The Pathology Institute, Tel Aviv Sourasky Medical Center, Sackler Faculty of Medicine, Tel Aviv University, Israel


    Abstract
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 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
The study was conducted to investigate the association of placental morphological and histopathological features with term, singleton pregnancies obtained by assisted reproductive technologies (ART). The study group comprised 45 consecutive women with a singleton pregnancy, obtained by ART, who delivered at term. For each subject in the study group, the consecutive, matched-for-age-and-parity woman, with a term singleton, spontaneously conceived pregnancy served as the controls. The placentae of both groups were subject to a detailed morphological and histopathological investigation by one pathologist, who was blinded to specimen origin. Pregnancy complications, fetal weight and perinatal outcome were similar in both groups. No differences in morphological or histopathological features of the placenta were observed between the groups. Nevertheless, the placentae of the study group showed a borderline, significantly higher placental weight and placental:fetal weight ratio, and placental thickness was significantly higher. Abnormal umbilical cord insertion was significantly more prevalent in the study group. Neither the specific ART method employed, nor the infertility factor affected the results, suggesting that multiple embryo transfers and/or ovulation induction protocols may account for these differences.

Key words: assisted reproductive technology/embryo transfer/ICSI/perinatal outcome/placental pathology


    Introduction
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
Several studies have shown singleton pregnancies, obtained by assisted reproduction technologies (ART) to be gestations of high risk (Doyle et al., 1992Go; Wang et al., 1994Go; FIVNAT, 1995Go; Tanbo and Abyholm, 1996Go), associated with an increased incidence of pregnancy-induced hypertension, placenta praevia, preterm delivery, Caesarean section, low-birth-weight and small-for-gestational-age (SGA) neonates. However, in most studies no difference in perinatal mortality or malformation rate was demonstrated (Doyle et al., 1992Go; Wang et al., 1994Go; FIVNAT, 1995Go; Tanbo and Abyholm, 1996Go). The reason for this less favourable outcome is unknown. Although women treated by ART tend to be `elderly' primiparae who are known to be in a high risk group (Kessler et al., 1980Go), several studies have also related pregnancy complication rates to the number of embryos transferred and with infertility diagnosis (MRC Working Party, 1990; Doyle et al., 1992Go; Wang et al., 1994Go). Nevertheless, various studies have demonstrated that infertility per se increases the risk of low birth rate, SGA and preterm birth (Tuck et al., 1988Go; Ghazi et al., 1991Go; Li et al., 1991Go; Williams et al., 1991Go). A recent study (Petersen et al., 1995Go) that compared the outcome of IVF pregnancies to those of infertile couples treated by non-IVF methods, found that IVF infants weighed 250 g less, which suggests that IVF may adversely affect the obstetric outcome. Pregnancies obtained by ART differ from normal pregnancies, in that more than one conceptus is transferred into the uterine cavity, the conceptus enters via the uterine cervix and reaches the uterus at least 2 days earlier than under normal conditions (Puissant et al., 1987Go; Barlow et al., 1988Go). Furthermore, the endometrium is exposed to high levels of oestrogen and progesterone, due to the ovulation induction protocols used in ART. Likewise, in pregnancies obtained by intracytoplasmic sperm injection (ICSI), both gametes are subject to external manipulation (Van Steirteghem et al., 1993Go). These differences may affect implantation and placentation and consequently, obstetric outcome. However, only a few studies (Englert et al., 1987Go; Burton and Saunders, 1988Go; Jauniaux et al., 1990Go; Gavriil et al., 1993Go; Williams and Jeffery, 1994Go) have investigated the morphological and histopathological features of placentae from pregnancies obtained through ART.

The purpose of the study was to make a prospective, random and blind comparison of the morphological and histopathological features of placentae of term, singleton, pregnancies obtained by ART [in-vitro fertilization (IVF) and embryo transfer and ICSI and embryo transfer] with those of matched pregnancies, conceived spontaneously.


    Materials and methods
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
Placentae obtained from 45 consecutive term (>36 weeks according to embryo transfer date) deliveries of singleton pregnancies, conceived by ART (IVF and embryo transfer, or ICSI and embryo transfer), comprised the study group. For each placenta obtained from an ART pregnancy, the placenta of the consecutive singleton, term, spontaneously conceived pregnancy, matched for maternal age and parity, served as a control. The placentae were subject to a detailed pathological investigation by one pathologist who was blinded to the origin of the specimen. Demographic and clinical data were extracted from maternal and neonatal medical records, as well as by patient interview. Multiple pregnancies, preterm deliveries and pregnancies complicated by early vanishing fetuses were excluded. The Institutional Review Board approved the study and informed consent was obtained from each patient.

Placental investigation included a detailed morphological evaluation that encompassed: placental shape, weight and thickness through a mid-placental section, and calculation of placenta:fetus weight ratio. Umbilical length and thickness were recorded, and umbilical cord insertion was divided into two categories: (i) normal, which comprised central and lateral cord insertion, and (ii) abnormal, which constituted marginal (<2 cm from the placental margin) and velamentous umbilical cord insertion (McLennan, 1968Go; Benirschke and Kaufmann, 1990Go; Altshuler, 1997Go). Following immediate macroscopic evaluation, the placentae were immersed in buffered 10% neutral formalin, and detailed microscopic evaluation was performed on several paraffin sections of each placenta, umbilical cord and membranes. Samples were obtained from tissues of both normal and abnormal appearance.

The histological examination embodied a careful evaluation of the trophoblast, decidua and blood vessels. Pathological abnormalities included: alteration of blood vessels (i.e. muscular hypertrophy of the media and fibrinoid changes in the vessel wall), inflammatory reactions (i.e. chorioamnionitis, villitis, villitis of unknown aetiology and funisitis), increased number of syncytial knots (>30%); changes in villous histology (i.e. thrombosis, fibrosis and haemorrhage); infarctions (at least two infarcts of >=2 cm in diameter) and intervillous fibrin deposition (Benirschke, 1960Go; Benirschke and Kaufmann, 1990Go; Altshuler, 1997Go).

Statistical analysis was performed by {chi}2 and Fisher exact tests. The Student t-test and the one-way analysis of variance (ANOVA) were used to compare group means. Significance was assumed at P < 0.05.


    Results
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 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
Demographics and relevant clinical data are depicted in Table IGo. As expected from the recruitment criteria, the mean gestational age, maternal age and parity were comparable. Pregnancy complications, mode of delivery and fetal weight were similar in both groups. No 5 min Apgar score of <7, or major congenital malformations were observed in either group.


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Table I. Clinical and demographic data of the study and control groups
 
Placental morphological and histopathological features are presented in Table IIGo. A higher mean placental weight and placenta:fetal weight ratio (P = 0.6 and 0.08 respectively) and significantly higher (P = 0.02) mean placental thickness were observed in the study group. Furthermore, the incidence of abnormal cord insertion (marginal and velamentous) was significantly higher in the study group (P = 0.03). Nevertheless, no significant differences were observed in other placental, morphological or histopathological features between the groups.


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Table II. Pathological features of placentae from the study and control groups
 
Of the study group, 24 women were treated by IVF and embryo transfer, while the ICSI and embryo transfer procedure was performed in 21 women (Table IGo). IVF and embryo transfer was used in most patients with unexplained infertility and mechanical factor, while ICSI was the primary method employed in patients with male factor infertility (data not presented). However, neither the ART method employed, nor the specific infertility factor affected the various placental features studied.


    Discussion
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 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
Only a few studies in the associated English literature have investigated the relationship between pregnancies obtained by ART and placental pathology (Englert et al., 1987Go; Jauniaux et al., 1990Go; Gavriil et al., 1993Go; Williams and Jeffery, 1994Go). Englert et al. (1987), in a non-controlled study, compared the placental morphology of pregnancies comprising 63 singletons, 15 twins, one triplet and one quadruplet obtained by IVF and embryo transfer, with data of normal pregnancies taken from the literature. These authors (Englert et al., 1987Go) observed a significantly higher frequency of marginal (15%) and velamentous (14%) cord insertion among placentae of pregnancies obtained by IVF and embryo transfer. A further non-blinded, controlled study from the same group (Jauniaux et al., 1990Go) compared 50 placentae of singleton term pregnancies obtained by IVF and embryo transfer with matched spontaneous pregnancies. They reported a significantly higher incidence of abnormal placental shape and marginal cord insertion among the IVF and embryo transfer groups (Jauniaux et al., 1990Go). These authors (Englert et al., 1987Go; Jauniaux et al., 1990Go; Gavriil et al., 1993Go) postulated that their results may reflect a problem of early placentation, most probably related to intrauterine embryo transfer, that may interfere with proper blastocyst/endometrial orientation, polar trophoblast differentiation or superficial implantation (McLennan, 1968Go) in pregnancies obtained by IVF and embryo transfer.

In comparison with our study, previous studies were either non-controlled (Englert et al., 1987Go) or not randomly and blindly performed (Englert et al., 1987Go; Jauniaux et al., 1990Go; Gavriil et al., 1993Go; Williams and Jeffery, 1994Go). Furthermore, in none of these studies (Englert et al., 1987Go; Jauniaux et al., 1990Go; Gavriil et al., 1993Go) was the histopathological evaluation performed by the same pathologist, and placentae of pregnancies obtained by ICSI and embryo transfer were not investigated.

In accordance with other authors (Englert et al., 1987Go; Jauniaux et al., 1990Go; Gavriil et al., 1993Go), we observed a higher incidence of abnormal umbilical cord insertion in placentae of ART-conceived pregnancies.

These findings suggest that term pregnancies obtained by ART may be at increased risk for the adverse consequences associated with abnormal cord insertion, such as vasa praevia, fetal haemorrhage and fetal anomalies (McLennan, 1968Go; Burton and Saunders, 1988Go; Benirschke and Kaufmann, 1990Go). Although in this study both groups had a similar perinatal outcome, a larger study is required to detect significant differences in perinatal variables. Likewise, these results may support the theory of abnormal blastocyst–endometrial orientation in ART-obtained pregnancies, as suggested by other authors (Englert et al., 1987Go; Jauniaux et al., 1990Go; Gavriil et al., 1993Go).

Abnormal blastocyst–endometrial orientation may be a result of embryo injection into the endometrium during embryo transfer. However, even a properly performed embryo transfer results in earlier placement of the embryo in the uterine cavity by 2 days. Proper attachment and implantation depends on an exact sequence of molecular events (Sueoka et al., 1997Go) that occur in the embryo and endometrium. The earlier presence of the embryo in the uterus may disturb the process of polar trophoblast differentiation, and proper blastocyst–endometrial orientation.

Nevertheless, the similar incidence of placental malformation in both groups does not support superficial placentation in ART pregnancies, as suggested by others (Englert et al., 1987Go; Jauniaux et al., 1990Go; Gavriil et al., 1993Go).

In both groups, the mean placental weight was within normal limits (<600 g) (Altshuler, 1997Go). However, there was an apparent trend towards a higher mean placental weight and placental:fetal weight ratio in the study group. Since these differences were neither related to the ART procedure, nor to the infertility aetiology, we may postulate that common factors, such as the ovulation induction protocols and multiple embryo transfer used during ART, may account for these differences. One possible explanation may be that endometrial hyperstimulation caused by the high oestrogen and progesterone levels, coupled with multiple embryo transfer, may induce more extensive pregnancy-related endometrial alterations (histologically and biochemically). This may result in an increased placental:fetal weight ratio and placental thickness, provided a singleton pregnancy results. Furthermore, this professed enhanced stimulation of the endometrium may improve the implantation of a singleton pregnancy, and the prospect of reaching term may be better. This assumption is supported by the observed similar pregnancy complication, perinatal outcome and placental histopathological features in these randomly selected matched groups.

Interestingly, in a recent study, Ribbert et al. found higher human chorionic gonadotrophin (HCG) levels in pregnancies obtained through IVF (Ribbert et al., 1996Go). Since the levels of HCG may reflect placental mass, our finding of apparently increased placental weight in these pregnancies may explain the elevated HCG concentrations. According to our results, neither the specific ART method employed, nor the infertility aetiology had any effect on placental morphological or histopathological features, or on maternal or neonatal outcome. Therefore, it seems that neither infertility per se (Tuck et al., 1988Go; Ghazi et al., 1991Go; Li et al., 1991Go; Williams et al., 1991Go) nor ART itself (Petersen et al., 1995Go) contribute to the adverse outcome in term, singleton, ART-obtained pregnancies through impaired placentation (Doyle et al., 1992Go; Wang et al., 1994Go; FIVNAT, 1995Go; Tanbo and Abyholm 1996Go).

Furthermore, according to our study, if maternal age and parity is controlled, the outcome of these pregnancies is similar to spontaneously conceived pregnancies, although this should be confirmed in a larger investigation.

In conclusion, we found that placentae of term ART-conceived pregnancies are thicker, seem to be heavier and to have a higher incidence of abnormal cord insertion than placentae of spontaneously conceived pregnancies. Since these differences were not related to the specific ART method employed, or infertility factor, our findings suggest that these differences may be related to multiple embryo transfer, and/or to the non-physiological hormonal milieu resulting from ovulation induction protocols used in ART.


    Notes
 
4 To whom correspondence should be addressed, at: Sara Racine IVF Unit, Tel Aviv Sourasky Medical Center, 6 Weizman Street, Tel Aviv 64239, Israel Back


    References
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 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
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Submitted on June 24, 1998; accepted on December 21, 1998.