
University of Newcastle, Leazes Wing, Royal Victoria Infirmary, Newcastle upon Tyne
National Teratology Information Service, Regional Drug and Therapeutics Centre Wolfson Unit, Newcastle upon Tyne
University of Newcastle, Leazes Wing, Royal Victoria Infirmary, Newcastle upon Tyne
National Teratology Information Service, Regional Drug and Therapeutics Centre Wolfson Unit, Newcastle upon Tyne
University of Newcastle, Leazes Wing, Royal Victoria Infirmary, Newcastle upon Tyne, UK
Correspondence: R. H. McAllister-Williams, Psychiatry, Leazes Wing, Royal Victoria Infirmary, Newcastle upon Tyne, UK. Email: R.H.McAllister-Williams{at}ncl.ac.uk
J.J.N. has received consultancy fees from Eli Lilly. S.H.T. has undertaken consultancy work for Lundbeck (their product sertindole does not feature in the data-set) and has current (non-psychiatric) research funded by BMS. P.R.M. has received honoraria for speaking engagements from Eli Lilly and Janssen-Cilag, which have been used for educational purposes. R.H.M-W has received honoraria for speaking engagements and attendance at advisory boards for a number of pharmaceutical companies manufacturing antipsychotic drugs, including Janssen-Cilag, AstraZenecca, Eli Lilly and Bristol-Myers Squibb.
See editorial, pp.
321–322, this
issue. ![]()
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The effects of in utero exposure to atypical antipsychotics on infant birth weight are unknown.
Aims
To determine whether atypical and typical antipsychotics differ in their effects on birth weight after maternal exposure during pregnancy.
Method
Prospective data on gestational age and birth weight collected by the National Teratology Information Service for infants exposed to typical (n=45) and atypical (n=25) antipsychotics was compared with data for a reference group of infants (n=38).
Results
Infants exposed to atypical antipsychotics had a significantly higher incidence of large for gestational age (LGA) than both comparison groups and a mean birth weight significantly heavier than those exposed to typical antipsychotics. In contrast those exposed to typical antipsychotics had a significantly lower mean birth weight and a higher incidence of small for gestational age infants than the reference group.
Conclusions
In utero exposure to atypical antipsychotic drugs may increase infant birth weight and risk of LGA.
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Infants born large for gestational age (LGA) are associated with an increased risk of complications to both mother and neonate. Maternal complications of larger birth weights at delivery may include vaginal lacerations,6 post-partum haemorrhage7 and a higher probability of emergency Caesarean delivery.8 In the neonate, risks include birth trauma, shoulder dystocia and foetal hypoxia.9,10 There are also long-term health implications, since being born LGA, independent of complications in delivery, is also associated with a predisposition for increased body mass index (BMI) and diabetes in later life.11,12 Predisposing factors for LGA birth include maternal obesity, type I diabetes, gestational diabetes and excessive maternal weight gain.13–16 All these conditions may be precipitated or exacerbated by use of atypical antipsychotics in non-gravid populations.
Yaeger et al17 highlighted the lack of data on antipsychotic drug usage in pregnancy that can be used to guide clinical decisions. Randomised controlled trial data of drug use in pregnancy will always be rare or non-existent because of ethical constraints.18 As a result, the best available data in this area tend to come from non-randomised prospective observational studies. Such studies are usually limited in the degree to which confounding variables are controlled for. Nevertheless, they provide an important information source for clinicians in the absence of more controlled studies. To investigate the hypothesis that birth weight would be increased by in utero exposure to atypical antipsychotic drugs, we conducted an observational study comparing the birth weights and gestational ages of infants exposed to atypical antipsychotics with a group exposed to typical antipsychotics and a reference group. This is the first such prospective study comparing infants born to mothers exposed to typical and atypical antipsychotics.
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Data requested include gestational age and weight at birth. The extent of data collection is limited to that which the clinician is able to provide when contacted by the NTIS. The NTIS have previously published on the safety of other agents in pregnancy from cases in the UK and through collaboration with other national information services.19–22 A search was conducted of the NTIS database between January 1995 and July 2006 for prospective cases (i.e. enquiry made prior to birth) involving maternal antipsychotic exposure.
For a reference group, the database was searched for a list of drugs compiled by the NTIS considered to be non-teratogenic and with no associated foetal or adult weight side-effects. These drugs were predominantly antihistamines, antibiotics, laxatives, β2-agonist inhalants, astringents, proton pump inhibitors and antimalarials. All cases of exposure to monotherapy with these agents were extracted for use as a reference group.
Inclusion and exclusion criteria
Only babies born after full-term (37 weeks gestation) deliveries to mothers
exposed to antipsychotics in therapeutic doses or one of the reference
medications were included in the analyses. Postdate deliveries (gestational
age >42 weeks) were excluded. For the antipsychotic groups, cases of
monotherapy with a single antipsychotic and antipsychotic exposure with more
than a single therapeutic agent (including over-the-counter medicine) were
included. Medications given in multiple drug exposures were not necessarily
given concurrently but there was exposure to more than one drug during the
pregnancy. However, cases where exposure occurred to both a typical and
atypical antipsychotic were not included. Exclusion criteria were if the
infant displayed congenital malformations, maternal diabetes was recorded or
if there was missing birth weight, gestational age or gender data.
Analyses
The numbers of LGA and SFD infants were compared between groups (maternal
exposure to atypical or typical antipsychotics and the reference group). Large
for gestational age was defined as a birth weight above the 90th percentile
for gestational age. In contrast, SFD was defined as a birth weight under the
10th percentile for that gestational age. Mean birth weight and gestational
age were compared between exposure groups. Gender-specific comparisons of mean
gestational age and mean birth weight were also performed.
In addition to analysis of the entire data-set, an analysis was conducted that excluded cases where concomitant exposure to potentially weight-altering medications (excluding antipsychotics) had occurred. Whether a drug was associated with weight gain or loss was judged on a case-by-case basis by an independent specialist with no knowledge of the patients or the antipsychotic that was taken.
Categorical outcomes (LGA, SFD, prematurity, postdatism) were compared using chi-squared analysis or Fisher exact test. Continuous data (birth weight and gestational age) were compared between groups using one-way analysis of variance followed by post hoc least significance difference analyses when data were normally distributed. Where data were not normally distributed, the Kruskal–Wallis test was used followed by independent sample Mann–Whitney U-tests. Normality of distribution was examined using the Kolmogorov–Smirnov test. SPSS version 12 for Windows was used for all statistical analysis. All tests were two-tailed.
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Of the remaining sample, 45 (53% males) were exposed to typical
antipsychotics (10 monotherapy), 25 (24% males) to atypical antipsychotics (10
monotherapy) and 38 (38% males) to reference agents. The distribution of cases
for each antipsychotic drug can be seen in
Table 1. Mean maternal age was
not significantly different between the typical (31 years, s.d.=6), atypical
(31 years, s.d.=5) and reference (31 years, s.d.=5) exposure groups
(P>0.5). Mean number of previous children was also comparable
between the typical (1 child, s.d.=1), atypical (1 child, s.d.=1) and
reference (2 children, s.d.=2) exposure groups (P>0.5). Three
infants in the atypical antipsychotic exposure (12%), four in the typical
antipsychotic exposure (9%) and one in the reference group (3%) displayed mild
transient neonatal problems (e.g. jaundice). These were within expected
incidences and there were no significant differences between groups in the
rates of these problems. Gestational age was not normally distributed in all
samples so non-parametric tests were used. A main effect of type of exposure
was observed for gestational age in the overall analysis (
=7.53, d.f.=2,
P<0.05).
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View this table: [in a new window] | Table 1 Number of mothers using each antipsychotic drug, including and excluding cases of polytherapy with a potentially weight-altering medication |
Independent sample Mann–Whitney tests revealed that infants exposed to typical antipsychotics had a significantly shorter gestational age than infants exposed to reference agents (median=273 and 280 days respectively; P<0.01). Gender-specific comparisons demonstrated that this effect was statistically significant for males (P<0.01) but not females. These differences remained when mothers exposed to weight-altering medications were excluded. There was no significant difference in gestational age between the atypical antipsychotic exposure group and the typical antipsychotic or reference group.
Birth-weight data were normally distributed in all samples for analysis. A main effect of type of exposure was observed for birth weight in the overall analysis (F=3.58, d.f.=2, P<0.05). This effect remained if pregnancies exposed to other potentially weight-altering medications were excluded from analysis. Post hoc (least significance difference) analysis revealed that infants exposed to typical antipsychotics weighed significantly less than infants in both the atypical antipsychotic (P<0.05) and reference groups (P<0.05). Gender-specific comparisons demonstrated that this was because female infants exposed to typical antipsychotics weighed significantly less than infants in both the atypical antipsychotic (P<0.05) and reference (P<0.05) groups. When mothers exposed to potentially weight-altering medications were excluded all significant differences remained apart from that between the typical antipsychotic and reference group (Table 2).
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View this table: [in a new window] | Table 2 Comparisons of mean birth weight between groups |
Large for gestational age
There were significantly more LGA infants in the atypical antipsychotic
exposure group (5/25; 20%) than in both the typical antipsychotic exposure
group (1/45; 2%; P<0.05) and the reference group (1/38; 3%;
P<0.05), even after mothers exposed to concomitant potential
weight-altering medication were excluded. For this latter analysis, the
proportion of LGA infants was 4/15 (27%) in the atypical antipsychotic group
and 0/22 in the typical antipsychotic group (P<0.05). Three of the
five LGA infants in the atypical antipsychotic group were above the 98th
percentile for their gestational age compared with none in the other two
groups. Medications taken by mothers of LGA infants are reported in
Table 3.
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View this table: [in a new window] | Table 3 Medications taken in cases where infants were large for gestational age and small for gestational age |
Small for date
There was no significant difference in the number of SFD infants between
the atypical antipsychotic group (2/25; 8%) and the typical antipsychotic
group (7/45; 16%; P40.1) or reference group (0/38;
P>0.5), even after mothers exposed to concomitant potential
weight-altering medication were excluded. In contrast, there were
significantly more SFD infants in the typical antipsychotic group than in the
reference group (P<0.05). However, with the exclusion of mothers
exposed to potential weight-altering medication this difference was no longer
significant with the proportion of SFD infants in the typical antipsychotic
group changing to 2/22 (9%). Of the SFD infants with typical antipsychotic
exposure, one was below the 2nd percentile compared with none of the SFD
infants in the atypical antipsychotic or reference groups. Medication exposure
for the SFD infants is reported in Table
3.
Exposure to olanzapine or clozapine
There were 16 infants exposed to either olanzapine or clozapine (13% male).
It was not deemed suitable to examine other types of atypical antipsychotics
as only 9 cases remained. The gestational age of those exposed to olanzapine
or clozapine was not significantly different from the typical antipsychotic
and reference groups, whereas a main effect of type of exposure was observed
for birth weight (F=3.37, d.f.=2, P<0.05). Post
hoc (least significance difference) analysis revealed infants exposed to
olanzapine or clozapine weighed significantly more than infants in the typical
antipsychotic group (P<0.01) but not the reference group
(P>0.05) (Table 3).
All differences remained when mothers exposed to potentially weight-altering
medication were excluded. Numbers were too small for gender-specific
comparisons of gestational age and birth weight. Of the 16 infants exposed to
olanzapine or clozapine, 5 were LGA (31%). This was significantly more than in
both the typical antipsychotic and reference exposure groups
(P<0.01 in both comparisons). When mothers exposed to concomitant
potential weight-altering medication were excluded, the proportion changed to
4 out of 12 (33%), which remained significantly more than in the typical
antipsychotic (P<0.05) and reference (P<0.01)
groups.
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In contrast, the typical antipsychotic groups significantly higher incidence of SFD infants than the reference groups and its lower mean birth weight than both the reference and atypical antipsychotic groups is consistent with previous findings. This further supports the hypothesis that atypical antipsychotic-induced weight gain in utero is attributable to the medication and not a facet of the illnesses being treated with antipsychotic medication. However, there were insufficient data in the NTIS database to allow a comparison of diagnoses of the mothers in the two antipsychotic groups and so this conclusion needs to remain tentative.
An earlier prospective study examined birth weights after maternal exposure to atypical antipsychotics by comparing infants with those of mothers who took a non-teratogenic agent.23 In contrast to the present study, this found no significant difference in mean birth weight between groups but found a significantly higher rate of SFD infants in the atypical antipsychotic exposure group. However, this earlier study did not exclude infants displaying congenital malformations and neonatal problems which may have been associated with being SFD irrespective of medication. Further, no adjustment for infant gender was made and the ratio of male:female infants was not stated. Effects of gender could have masked effects of differences in mean birth weight.24 In our study, there was a higher proportion of male infants in the typical antipsychotic group (53% v. 37%), which would be expected to bias this group towards being heavier.
Limitations
Our study has a number of limitations. In many cases, the NTIS had not
received information on variables that may affect birth weight such as
maternal weight, multiparity, and maternal cigarette and alcohol use. Smoking
and alcohol misuse are likely to reduce birth weight and to be more prevalent
in women with psychiatric disease compared with the reference group. This
would tend to mask rather than enhance any weight differences associated with
atypical antipsychotic exposure.
However, smoking and alcohol use may contribute to the lower birth weights observed in the typical antipsychotic group. Information regarding exact dosing and trimester of exposure to antipsychotics was often not provided consistently and so no conclusions could be drawn regarding these factors. The small number of infants included in the study means that the proportion of males to females was unequal between exposure groups and there were limited cases of atypical antipsychotic exposure in male infants. Gestational age was significantly higher in the reference group, which may have biased the group towards being heavier although this difference was, at most, a weeks gestation.
Care also needs to be exercised in the interpretation of the data owing to the possibility of cohort effects. The data were collected over an 11.5-year period. It might be expected that proportions of typical and atypical exposures varied over this time. Given that there has been an increase in maternal weight over recent years,25 it is possible that this has contributed to the increased rate of LGA babies found in those exposed to atypical compared with typical antipsychotics. Further, there is a potential issue with the small number of cases meeting our inclusion criteria in the NTIS database (86) over this period of time, which raises questions regarding the nature of these mothers and the clinicians contacting the NTIS. This was an important reason why only prospective data were examined. With regard to the issue of power, LGA is defined as being a birth weight above the 10th percentile. For reference, a sample size of 41 would be required for an 80% power of detecting an increase in the LGA rate to 25% with P<0.05. However, note that as expected, the rates of LGA births among the babies exposed to typical antipsychotics was lower than 10% and that a sample size of just 26 is required for an 80% power of detecting a difference of LGA from 5% to 20% with P<0.05. This study had sample sizes of 25 in the atypical, 45 in the typical and 38 in the reference groups.
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Such studies require a more systematic collection of data from representative cohorts, ideally mothers with severe mental illnesses on no medication and those on antipsychotic monotherapy. Data collection needs to include more information than currently available regarding the dose of drug used, the timing of exposure during pregnancy and maternal diagnosis, as well as information regarding potential confounders, including maternal smoking status, alcohol usage, weight and physical health. The effects of potential increases in birth weight in babies exposed in utero to atypical antipsychotics on the longer-term health of the offspring are currently unknown and further studies are needed to explore these issues. The available data are insufficient to justify wholesale changes in prescribing recommendations5 but do point to the need for careful monitoring of foetal growth in pregnant women prescribed atypical antipsychotics. Although there are risks associated with an infant being born SFD, switching a mother from a typical antipsychotic to an atypical with the sole intention of increasing the babys birth weight is not clinically justified because of the lack of an understanding of the long-term consequences of in utero exposure to an atypical plus the risks of destabilising the mothers illness by switching treatments.
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