1 Center for Reproductive Medicine, Department of Obstetrics and Gynecology, 2 Department of Public Health and 3 Department of Clinical Genetics, Academic Medical Center, University of Amsterdam, P.O.Box 22700, 1100 DE Amsterdam, The Netherlands
4 To whom correspondence should be addressed at: Center for Reproductive Medicine, Department of Obstetrics and Gynaecology (H4-205), Academic Medical Center, University of Amsterdam, P.O. Box 22700, 1100 DE Amsterdam, The Netherlands. e-mail: M.Goddijn{at}amc.uva.nl
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Abstract |
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Key words: maternal age/repeated miscarriage/structural chromosome abnormalities/translocation/unbalanced chromosome abnormalities
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Introduction |
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Epidemiological evidence shows a steep increase in sporadic miscarriage rate in women aged 36 years (Cowchock et al., 1993
; Smith and Buyalos, 1996
; Nybo Andersen et al., 2000
; Bricker and Farquharson, 2002
; De la Rochebrochard and Thonneau, 2002
). This age-related risk is due to a higher number of aneuploidies, mainly trisomies (Hassold and Chiu, 1985
; Kratzer et al., 1992
; Hassold and Hunt, 2001
; Robinson et al., 2001
). The age-dependent increase of trisomies, with repeated miscarriage as its manifestation, may be due to a recurrence of sporadic chromosome abnormalities (Robinson et al., 2001
). Women with repeated miscarriage and aged
36 years tend to have a lower frequency of euploid miscarriage (Stephenson et al., 2002
).
In The Netherlands, women with repeated miscarriage and aged 36 years are eligible for prenatal diagnosis, in addition to parental karyotyping. The effectiveness of offering women both screening programmeskaryotyping for parental carrier status and prenatal chromosome studies of the fetusto this group of women is unknown.
The aim of this study was to determine clinical consequences of diagnosing structural chromosome abnormalities in couples with repeated miscarriage. We therefore determined frequency of carrier status and frequency of unbalanced offspring after establishing carrier status.
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Materials and methods |
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Carriers and non-carriers were contacted by mail with an invitation to participate in the study, and informed consent was obtained. Reminders were sent out in cases of non-response.
Data were retrieved from medical records and telephone interviews, and focused on the parental characteristics at the time of the chromosome analysis, the previous miscarriages, obstetric history and obstetric outcome for 2 years after chromosome analysis.
Outcome measures were live-born handicapped childreneither caused by a structural chromosome imbalance or notlive-born healthy children, the occurrence of a subsequent miscarriage, and induced abortion because of a structural chromosome imbalance.
Institutional Review Board approval was obtained.
Cytogenetic analysis
Chromosome preparations were obtained from peripheral blood lymphocyte cultures. Five GTG-banded metaphases (minimal 500 band level) were evaluated for each of the individuals.
Statistical analysis
The cohort under study was subdivided into couples who were ascertained after two, three or four and more miscarriages. The numbers of carriers and non-carriers were calculated. Thereafter, these numbers were broken down according to maternal age <36 and 36 years. Odds ratios (OR) and 95% confidence intervals (CI) were calculated to establish a difference of risk on being a carrier in these two age groups. Statistical significance was defined as confidence intervals that did not include 1.0. Statistical analysis was performed with the Statistical Package for the Social Sciences 11.0 (SPSS Inc., USA).
Numbers of carrier and non-carrier couples in subgroups of the study population were multiplied to the original level of the screening population (i.e. 51 carrier couples and 1273 non-carrier couples) to provide a projected prevalence figure.
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Results |
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Eight extra non-carrier couples were excluded, five couples because one parent or semen donor was not karyotyped, two couples because of sex chromosome mosaicism in the female, and one couple because the father was detected to be carrier of a structural chromosome abnormality only after the birth of a child with congenital abnormalities.
A total number of 115 couples remained for analysis, which consisted of 41 couples including one carrier and 74 non-carrier couples.
In 101 couples, the country of birth was The Netherlands (88%). In the 14 other couples, the remaining countries of birth were Surinam (n = 4), Turkey (n = 3), Curaçao (n = 2), Africa (n = 2), and other countries (n = 3). The mean age of the women at time of karyotyping was 34.2 years (range 22.346.4). A non-significant difference in mean maternal age was found between the carrier couples (33.2 years, range 22.343.6) and the non-carrier couples (34.7 years, range 23.546.4) (P = 0.31). The mean age of men at time of karyotyping was 35.3 years (range 19.245.7). A non-significant difference in mean paternal age was found between the carrier couples (34.8 years, range 19.245.4) and the non-carrier couples (35.6 years, range 25.145.7) (P = 0.27). First-degree cousins were found in one carrier couple and in two non-carrier couples.
The couples were referred from four sources: 56 couples were referred by an academic gynaecologist (48.7%), 54 couples by a gynaecologist from a general hospital (47.0%), three couples by a midwife (2.6%) and two couples by a general practitioner (1.7%).
Outcome of cytogenetic analysis
The structural chromosome abnormalities of the 41 carrier couples are listed in Table I. We found more female carriers (n = 27) than male carriers (n = 14). There were 26 reciprocal translocations (63.4%), five pericentric inversions (12.2%), four paracentric inversions (9.8%), three Robertsonian translocations (7.3 %), two (Y;22) translocations (4.9%) and one marker chromosome (2.4%).
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Obstetric history
Before karyotyping, the 41 carrier couples had had 160 pregnancies, and the 74 non-carrier couples 286 pregnancies. The mean number of pregnancies per couple before karyotyping was the same for carrier couples (3.9; range 211) and non-carrier couples (3.9; range 210).
Nearly half of the couples had had two miscarriages (55/115 = 48%), 40 couples had had three miscarriages (40/115 = 35%) and 20 couples had had four or more miscarriages (20/115 = 17%). The highest number of miscarriages was 10. Out of 41 carrier couples, 18 couples (44%) were ascertained after two miscarriages, 15 couples (37%) after three miscarriages and eight couples (20%) after four and more miscarriages. Out of 74 non-carrier couples, 37 couples (50%) were ascertained after two miscarriages, 25 (34%) couples after three miscarriages and 12 couples (16%) after four and more miscarriages.
The mean gestational age was 9.0 weeks in carriers (n = 124 miscarriages, range 419 weeks) and 8.6 weeks in non-carrier couples (n = 211 miscarriages, range 519 weeks). No statistically significant differences in carrier status were found between couples with three miscarriages versus couples with two miscarriages (ratio of carrier/non-carrier couples was 15/25 and 18/37 respectively, OR 1.2, 95% CI 0.52.9), and between couples with four and more miscarriages versus couples with three miscarriages (ratio of carrier/non-carrier couples was 8/12 and 15/25 respectively, OR 1.1, 95% CI 0.43.3). The same holds for being a carrier in couples with three or more miscarriages versus two miscarriages (ratio of carrier/non-carrier couples 23/37 and 18/37 respectively, OR 1.3, 95% CI 0.62.8).
Maternal age
The OR of being a carrier aged <36 years at last miscarriage and 36 years at last miscarriage calculated for the whole group was 1.7 (95% CI 0.74.2), which implies that the risk of being a carrier is not significantly different when maternal age is <36 years. Ascertainment after two, three or more miscarriages did not change these OR significantly (Table II).
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Obstetric outcome in carrier couples
The mean duration of follow-up for carrier couples was 71.7 months, range 25118 months.
After ascertainment of carrier status, a total number of 43 pregnancies was established in 25 carrier couples who wanted a child. Of these 43 pregnancies, 30 resulted in a live-born healthy child (70%), 11 resulted in a miscarriage (26%), one pregnancy was ongoing (2%), and one pregnancy with a DandyWalker malformation was reported (2%). Prenatal diagnosis was performed in 26 pregnancies. In 15 pregnancies (58%) a normal karyotype was found, in the remaining 11 pregnancies (42%) a balanced karyotype related to the parental carrier was obtained. Mean maternal age at time of prenatal diagnosis was 33.0 years (range 2244). The fetal DandyWalker malformation occurred in a couple in which the mother carried a paracentric inversion [46,XX ish inv(8)(p21p23)]. The pregnancy was terminated at 24 weeks.The chromosome diagnosis of the amniocentesis performed was a balanced paracentric inversion of chromosome 8 [karyotype: 46, XY,inv(8)(p21p23)] just like the mother, and seemed unrelated to the DandyWalker malformation.
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Discussion |
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To our knowledge, defining frequencies of carrier status of a structural chromosome abnormality in different maternal age groups has not been reported previously in couples with repeated miscarriage. The cohort under study was subdivided into groups who were ascertained after two, three or four and more miscarriages. Carrier frequency was established for the respective subgroups and further subdivided into two maternal age groups, <36 years at last miscarriage before ascertainment and 36 years at last miscarriage before ascertainment. The risk of being a carrier for this cohort was not statistically proven to be lower (as might be expected) when maternal age was
36 years. Nor could we find a higher risk of being a carrier with increased number of previous miscarriages.
With this study we aimed at finding a subgroup with apparently low frequency of carrier status, but until now did fail to detect such a subgroup.
In a larger study population, subgroups can probably be traced with a low frequency of carriers. A larger study can also give the opportunity to calculate a spline function and possibly reveal an alteration in pattern of decline of carrier status at increasing maternal age.
Many studies which describe frequencies of carrier status of structural chromosome abnormalities in couples with repeated miscarriage do report obstetric history, but data about obstetric follow-up is limited. We found three relatively small studies in which registration of subsequent pregnancies in cases of carrier status and repeated miscarriage took place. No unbalanced reproductive outcome was reported in respectively 7, 35 and 17 carrier couples with repeated miscarriage (FitzSimmons et al., 1983; Sachs et al., 1985
; Fortuny et al., 1988
). These studies favour a normal pregnancy outcome in carriers who were traced after the occurrence of miscarriages. The results of our study, with an even higher number of carriers, i.e. 41, are in concordance with their findings.
The risk of having a handicapped child with an unbalanced karyotype depends on the type of translocation, and on the sex of the transmitting parent (Madan, 1995; Geraedts, 1996
; Gardner, 1996
, p. 38). Generally a 510% risk of a live-born child with multiple congenital abnormalities is mentioned in cases of carrier status (Gardner, 1996
, p. 59). Given a 510% risk figure of a live-born child with multiple congenital handicaps, in our study population three live-born children with multiple congenital handicaps would be expected (43 pregnancies in carrier couples multiplied by 0.075). But, beside a case with DandyWalker malformation, most probably unrelated to the parental carrier status, in our study population no children with handicaps were born out of a total number of 43 pregnancies.
The risk that parents will bear offspring with an unbalanced chromosome complement depends, apart from the sex of the carrier and type of rearrangement as stated above, on the method of ascertainment (Hsu, 1998). The frequencies of unbalanced reciprocal translocations at prenatal diagnosis in subsequent pregnancies are much higher when a family is ascertained through prior full-term unbalanced progeny than when they are ascertained through repeated miscarriage: 19.8 versus 4.8% for maternal carriers; 22.2 versus 1.4% for paternal carriers (Daniel, 1989
) and 20.8 versus 3.4% for both maternal and paternal carriers (Boué and Gallano, 1984
). In one case in our study group, the structural chromosome abnormality in the father, a 46,XY,inv(5)(p15.3q35) karyotype, was only detected following after the birth of a child with microcephaly, an atrial septal defect and a ventricular septal defect.
Whether our study population is a selection rather than a reflection of the whole population of couples with repeated miscarriage is difficult to determine. It is unlikely that couples with repeated miscarriage who are not referred for karyotyping have a worse obstetric history, thus reflecting a subgroup with translocations leading more often to unbalanced offspring.
In conclusion, the most striking finding was the non-existence of unbalanced offspring after detecting a structural chromosome abnormality. This finding needs to be confirmed in a larger multi-centre cohort. A nationwide study is currently underway in The Netherlands, which will probably enable us to draw further conclusions about the clinical significance of establishing parental karyotype in couples with repeated miscarriage.
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Acknowledgements |
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References |
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Submitted on October 31, 2003; accepted on January 15, 2004.