Evolution of perinatal depressive symptoms from pregnancy to two years postpartum in a low-risk sample: The MATQUID cohort

Journal of Affective Disorders 139 (2012) 23–29

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Evolution of perinatal depressive symptoms from pregnancy to two years postpartum in a low-risk sample: The MATQUID cohort A.L. Sutter-Dallay a, b,⁎, O. Cosnefroy b, d, E. Glatigny-Dallay a, H. Verdoux a, c, d, N. Rascle b, d a b c d

University Department of Adult Psychiatry, Charles Perrens Hospital, Bordeaux, France EA 4139, Bordeaux, France INSERM U 657, Bordeaux, France University Victor Segalen, Bordeaux, France

a r t i c l e

i n f o

Article history: Received 11 March 2011 Received in revised form 17 August 2011 Accepted 17 August 2011 Available online 11 March 2012 Keywords: Depressive symptoms Perinatal period Evolutionary profiles Risk factors

a b s t r a c t Background: Few studies have explored the evolution of perinatal depressive symptoms (PNDS) throughout the perinatal period. Aims: To evaluate in a low-risk sample, whether different evolutive profiles of PNDS exist from pregnancy to 2-years postpartum, and whether the subgroups differ regarding psychopathological and demographic characteristics. Methods: In a prospective, longitudinal study from 8 months pregnancy to 2 years postpartum, repeated measures of PNDS using the CES-D were performed on a sample of 579 women at low-risk for PNDS. First, semiparametric mixture models were used to identify groups of women with distinct trajectories of PNDS. Second, multinomial logistic regressions were used to identify risk factors for each group. Results: Four distinct trajectories of PNDS evolution were found: (i) 72% of the women never presented with clinically significant depressive symptoms; (ii) 4% presented with depressive symptoms only during the postnatal period; (iii) 21% presented with depressive symptoms throughout the follow-up period, with a higher intensity during pregnancy; (iv) 3% presented with stable highly intense symptoms throughout the follow-up period. Psychosocial risk factors for PNDS were mainly identified in the patients of the third group, with an influence of socioeconomical variables and anxiety traits. Limitations: The main limitations of the present study are the small size of the sample and the low level of risk for PNDS, so the results cannot be extrapolated to all types of populations. Conclusion: Different subtypes of evolutionary profiles of PNDS are found in a low-risk sample, and are associated with different profiles of risk factors. © 2011 Published by Elsevier B.V.

1. Introduction Variations in maternal mood during the transition to parenthood have been a focus of research and clinical attention for 40 years. Kumar and Robson (1984) showed that there were different types of evolution of emotional symptoms from

⁎ Corresponding author at: Réseau de Psychiatrie Périnatale, Pôle Universitaire de Psychiatrie de l'adulte, CH Charles Perrens, 121 Rue de la Béchade, 33000 Bordeaux, France. Tel.: + 33 556561782; fax: + 33 556561768. E-mail address: [email protected] (A.L. Sutter-Dallay). 0165-0327/$ – see front matter © 2011 Published by Elsevier B.V. doi:10.1016/j.jad.2011.08.018

pregnancy to postpartum. Although antenatal depressive symptoms appear to be strong predictors for postnatal depressive symptoms (Beck, 2001; O'Hara and Swain, 1996; Robertson et al., 2004), many perinatal studies have been cross-sectional. Some prospective studies have evaluated mood during pregnancy and the postpartum period (Andersson et al., 2006; Brooks et al., 2009; Edge, 2007; Evans et al., 2001; Glaser et al., 1998; Hay and Kumar, 1995; Heron et al., 2004; Homish et al., 2004; Kitamura et al., 2006; Kurstjens and Wolke, 2001; Moss et al., 2009; Murray, 1992; Murray et al., 1996; Petterson and Albers, 2001; Reay et al., 2011; Ross et al., 2004; Setse

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et al., 2009; Vesga-López et al., 2008) but most have studied postnatal maternal mood during the early post-partum (from 6 to 12 weeks) and once later on, generally between 6 and 12 months (for review see Gaynes et al., 2005). To our knowledge, only two studies have performed repeated evaluations in association with a methodology demonstrating different types of evolutionary profiles of depressive symptoms from pregnancy to several years post-partum (Mora et al., 2009; Seto et al., 2005). The work by Seto et al. (2005) confirmed their hypothesis of the existence of 4 distinct profiles of depressive symptoms from 18 months to 10 years post-partum: “never” depressed, depressed only at one phase, chronically mildly and chronically severely depressed. The last two “chronically depressed” groups presented significantly higher depression scores at the time of delivery. The second study by Mora et al. (2009) showed the existence of 5 distinct trajectories of perinatal depressive symptoms (PNDS) from pregnancy to 2 years postpartum. A group “never” depressed, a group depressed antepartum, a group depressed postpartum, a group chronically depressed from pregnancy to 2 years postpartum, and a group depressed after one year postpartum. Chronically depressed women more frequently lived alone, had lower educational level and income, had more children, and suffered from stress and anxiety. Finally, the large majority of the above mentioned studies assessed depressive symptoms among low-income populations, i.e. a particularly vulnerable population with regard to perinatal depressive symptoms (Beck, 2001; O'Hara and Swain, 1996; Robertson et al., 2004). Nevertheless, middleto-high social-economical groups, which are a priori at lower risk for perinatal mood disorders, are also concerned both by perinatal mood variations and their impact on the development of their children (Sutter et al., 1997, 2003; Sutter-Dallay et al., 2004, 2011; Verdoux et al., 2002). The aim of the present study was to determine in a middle-to-high social-economical status sample of women (i) whether it was possible to distinguish different evolutions of PNDS from the 3rd trimester of pregnancy until two years postpartum and (ii) whether differences exist between the subgroups regarding psychological and demographic characteristics.

psychiatric cares or prescription of long-acting antipsychotics); 4) neither multiple pregnancy nor in vitro fertilization for the current pregnancy; 5) less than one week of hospitalization for pregnancy complications; 6) no planned cesarean section delivery. These inclusion and exclusion criteria were designed to include a homogeneous sample of women with regard to gestational age, delivery conditions and psychiatric status; women were subsequently excluded after delivery in the case of premature birth or unplanned cesarean delivery. Of the 945 screened women fulfilling inclusion criteria, 366 women (38.7%) did not participate: 272 refused, mostly because the survey was considered as too time-consuming, 64 could not be contacted by phone, 11 women who initially agreed did not come to the baseline interview and 19 women did not complete the full questionnaire. The final sample includes 579 women. 2.2. Assessment The baseline interview during the 3rd trimester of pregnancy included collection of psycho-socio-demographic information. The existence of past personal history of depressive episode prior to pregnancy was evaluated through the following question: “Evaluated on the existence of a treatment or the impression that the disorders would have required care”. Except for the second interview, which took place at the maternity unit, the follow-up interviews took place at home. At each assessment including the one during pregnancy, a self-report questionnaire was given to the mothers. If mothers could not complete it during the visit, they were asked to return it by mail. This questionnaire included the CES-D (Fuhrer and Rouillon, 1989; Radloff, Table 1 Characteristics of sample. N = 579

Age

Mean

SD

29.37

4.33

N

%

Income in euros per month b 1500a ≥ 1500

166 413

28.68 71.32

The method of the MATQUID prospective survey has been previously presented (Verdoux et al., 2002). Briefly, research psychologists first assessed pregnant women during the 3rd trimester of pregnancy. Then, the mothers were assessed 8 times over a two-year follow-up period, after 8 months of pregnancy, at days three, six weeks, 3, 6, 12, 18 and 24 months after delivery.

Educational levela b High school diploma (HSD) HSD HSD + 1 to 3 N HSD + 3

82 89 221 185

14.21 15.42 38.30 32.06

Parityb 0 ≥1

373 204

64.64 35.36

2.1. Subjects

Marital statusb Married Other (including living together)

307 271

53.11 46.89

2. Method

Consecutive pregnant women attending antenatal clinics at the maternity units of the University Hospital of Bordeaux were included if they fulfilled the following criteria: 1) written informed consent to participate; 2) fluent in French; 3) living in the catchment area of the hospital (Bordeaux and neighboring suburbs); 4) no personal history of chronic severe mental illness (defined by past history of community

Past personal history of self-reported depressive episode Yes 102 No 477

17.61 82.39

SD: standard deviation. a Mean French salary at time of inclusion. b Numbers lower than total number of subjects are due to missing data.

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Table 2 Values of Bayesian Information Criteria (BIC), average estimated posterior probabilities (P) and size of groups in the process of model selection. Model

BIC

3 groups

− 9332.35

4 groups

5 groups

− 9274.68

− 9235.56

Number of groups

P N % P N % P N %

Total

G1

G2

G3

0.82 37 6.39 0.87 22 3.80 0.88 347 59.93

0.93 448 77.37 0.92 419 72.37 0.84 18 3.11

0.93 94 16.23 0.87 122 21.07 0.77 150 25.91

1977) to assess depressive symptoms and the Bonis Anxiety Trait-State Inventory (BATE) (De Bonis, 1973; De Bonis and Ferrey, 1975), “state” version for the evaluation of anxiety levels. The CES-D is a widely used self-report 20-item scale designed to measure levels of depressive symptoms in the general population, and which also has excellent psychometric properties in both clinical and epidemiological studies with diverse populations, including the perinatal period, as underlined by the report by Gaynes et al. (2005) concerning screening for perinatal depression. Possible scores range from 0 to 60, with higher scores reflecting higher levels of depressive symptoms in the past week; a cut-off of 16 or more has been defined as indicating a clinically significant level of depressive symptoms (Weissman et al., 1977). As is standard for this tool in clinical studies during the perinatal period (Beeghly et al., 2002; Fihrer et al., 2009; Horwitz et al., 2007; Mora et al., 2009; Setse et al., 2009), a cut-off score of 16 or higher was used in the present study as indicative of clinically significant level of depressive symptoms. The Bonis Anxiety Trait-State Inventory (BATE) (De Bonis, 1973; De Bonis and Ferrey, 1975) “trait” version was used to assess trait anxiety levels. This questionnaire incorporates 37 items, each graded from 0 (lowest severity) to 4 (highest severity), assessing psychological factors, somatic factors, and specific fears. An overall anxiety score was obtained as the sum of grades over all 37 items. This scale has good psychometric properties (De Bonis, 1973; De Bonis and Ferrey, 1975; Lerebours et al., 2007; Loonis et al., 2000) and allows a self-rating of trait anxiety.

G4

G5 579 100.00

0.92 16 2.76 0.85 59 10.19

579 100.00 0.99 5 0.86

579 100

group to which their posterior probability of belonging was the highest. Finally, a multinomial logistic regression yielding odds ratios (ORs) and 95% CI was used to identify possible risk factors for each trajectory. Potential predictive variables were chosen according to the literature and the available data: age, parity, income, marital status level of trait anxiety and past personal history of depressive episodes (self-evaluated by the existence of a treatment or by the feeling that a treatment would have been necessary). Owing to the small size of the sample and the strong colinearity between income and educational level, we excluded the latter from the model. These risk factors are time-stable covariates. They were introduced simultaneously in the analysis. 3. Results The sample was mainly composed of primiparous married women with good income, of good educational level, mostly having no past personal history of self-reported depressive episode (Table 1). 3.1. Selection and description of groups Models with 3 to 5 groups were analyzed (Table 2). By comparing BIC values, it appears that the 5-group model fits the data better than the other two. Similarly, in terms of average posterior probabilities, the 5-group solution also seems suitable because the average estimated for each group exceeds .70. However, in

2.3. Data analysis Data were analyzed in two steps. First, trajectories of depressive symptoms were modeled via the 8 scores on the CES-D corresponding to the two-year follow-up period. Semiparametric mixture models were estimated using PROC TRAJ procedure (Jones et al., 2001) with SAS Institute Inc (2006). This method is particularly well suited for identifying subgroups of subjects who followed distinct trajectories (Jones and Nagin, 2007; Nagin and Tremblay, 2001). It allows identification of the number of subgroups and estimates their trajectory shapes as well as the number of subjects per group. Given the nature of the scale, we used the CNORM model estimation. The Bayesian Information Criterion (BIC) governed selection of the optimal number of groups and the shape of the trajectories of each group (see Appendix 1). Then, as did Costello et al. (2008), subjects were assigned to the

Fig. 1. Trajectories of depressive symptoms (dashed confidence interval 95%).

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Table 3 Characteristics of different subgroups regarding variables included in regression model.

Age Trait anxiety score

Never (n = 419; 72%)

Postpartum (n = 22; 4%)

Antepartum (n = 122; 21%)

Chronic (n = 16; 3%)

Mean

SD

Mean

SD

Mean

SD

Mean

SD

29.32 25.18

4.16 12.87

31.05 19.95

3.86 9.19

29.39 37.22

4.66 14.71

28.06 62.64

01/06/27 23.56

N

%

N

%

N

%

N

%

Income b 1500

103

24.58

5

22.73

51

41.80

7

43.75

Parity 0 N=1

256 161

61.39 38.61

12 10

54.55 45.45

93 29

76.23 23.77

12 4

75 25

Marital status Married Other

236 183

56.32 43.68

12 10

54.55 45.45

51 71

41.80 58.20

8 7

53.33 46.67

Past personal history of self-reported depressive episode Yes No

61 358

14.56 85.44

3 19

13.64 86.36

32 90

26.23 73.77

6 10

37.50 62.50

terms of group size, this solution provides a group with 5 subjects corresponding to 0.86% of the total sample. We therefore opted for the 4-group model in which group size is satisfactory and whose average posterior probability shows a mean of 0.89. Furthermore, this solution fits the data better than the 3-group one and all its parameters (constant, linear, quadratic) are significant. Finally, the interpretation of the trajectories is consistent with the literature. Our solution is therefore composed of four groups (see Fig. 1). Group no 1, “Postpartum”, is composed of subjects whose level of depressive symptoms during the third trimester of pregnancy is the lowest of the sample (m= 6.71). This level tends to increase rapidly (slope= 1.08) and to reach a maximum 13.7 months after birth, with an average score of 15.21. Table 4 Multinomial regression model assessing characteristics of subjects in depressive symptoms groups (reference group “never”). Ora (95% CI)b Age

Trait anxiety score (per unit)

Income (b 1500 Vs N 1500)

Parity (0 vs ≥1)

Marital status (other vs married) Past personal history of self-reported depressive episode (yes vs no)

Postpartum Antepartum Chronic Postpartum Antepartum Chronic Postpartum Antepartum Chronic Postpartum Antepartum Chronic Postpartum Antepartum Chronic Postpartum Antepartum Chronic

⁎ p b .05. ⁎⁎ p b .001. a OR: odds ratio. b 95% CI = 95% confidence interval.

1.111 1.108⁎⁎ 1.094 0.967 1.061⁎⁎ 1.156⁎⁎

(0.988; (1.044; (0.912; (0.929; (1.043; (1.102; 0.916 (0.279; 2.229⁎⁎ (1.303; 0.88 (0.148; 0.1.168 (0.435; 1.948⁎ (1.102; 2.182 (0.394; 1.322 (0.516; 1.443 (0.874; 0.828 (0.177; 0.877 (0.244; 0.756 (0.423; 1.505 (0.315;

1.250) 1.177) 1.312) 1.006) 1.080) 1.213) 3.012) 3.813) 5.245) 3.138) 3.444) 12.073) 3.385) 2.383) 3.862) 3.159) 1.350) 7.188)

The quadratic term (−0.04) shows a very slight decrease in the level of depressive symptoms reaching an average of 11.06 after 24 months. Group no 2, “Never”, shows an average level of depressive symptoms during the last trimester of pregnancy of 14.28 with a low linear decrease (−0.07) to the level of group 1 after 24 months (m= 12.65). Group no 3, “Antepartum” starts with a high average level of depressive symptoms during pregnancy (m= 20.94) which tends to decrease (−0.52) until the 13th month after delivery and reaches a minimum average of 16.89. This group is also characterized by a very slight increase (0.02) leading to an average of 19.09 after 24 months. Finally, group no 4, “Chronic”, includes subjects with a stable and high mean level of depressive symptoms (m= 26.88) from the end of pregnancy to 2 years after birth. The confidence intervals do not overlap for groups 3 and 4, thus ensuring a clear distinction between the groups. Regarding groups 1 and 2, there is a crossover of trajectories showing that from the 5th month, these two groups show similar levels of depressive symptoms. Moreover, groups 1, 2 and 3 seem to present the same levels of depressive symptoms between months 12 and 16. Finally, to ensure that the estimations of the parameters of the slopes in groups 2 and 3 were significantly different from each other, we conducted a test of invariance (Jones and Nagin, 2007). This demonstrated a significant difference between the slopes of groups 2 and 3 (χ2 (1) = 36.74, p b .000). The slope of group 3 decreased significantly faster than that of group 2. 3.2. Multinomial regression The reference group to which the other three groups are compared is the group “Never” (Characteristics of the subgroups in Table 3). The model correctly fits the data (Wald χ2 (18) = 101.41, p b .0001). After adjustment for all covariates, older age, higher state anxiety score and low income remained significant risk factors. A one standard deviation (SD) increase in age was significantly associated with a 10.8% increase in odds of being in the antepartum sub-

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group compared with the “never” sub-group. Furthermore, a one SD increase on the trait anxiety scale was significantly associated with a 6.1% and a 15.6% increase in the odds of being in the antepartum group and chronic group, respectively. Finally, women whose income was lower than 1500 euro per month were more likely to be classified in the antepartum group versus the never group (Table 4). 4. Discussion In the present middle-to-high socioeconomic status population, a two-year follow-up of PNDS showed 4 groups with distinct trajectories, including two that reached clinical significance on the CES-D. Age, trait anxiety, low income and parity were risk factors for belonging to sub-groups of patients presenting with clinically significant depressive symptoms from pregnancy to the end of follow-up. In studies until now, Seto et al. (2005) validated their hypothesis of the existence of 4 evolutionary profiles of postnatal depressive symptoms by using the CES-D from 18 months to 10 years postpartum in a sample of 476 women. They showed that women mildly (3 or 4 CES-D scores between 16 and 24) or severely chronically depressed (≥25 3 or more times) during the years following birth had higher CES-D scores at delivery than women never depressed (CES-D scores always b16) or depressed only at one stage (one CES-D score ≥16). However, the methodology of that study did not allow direct comparison with the present one because of the presetting of depressive profiles, whose evaluation began 18 months postpartum, and because delivery data were considered in a second step for the purposes of group comparison. The other relevant study was the prospective observational one by Mora et al. (2009) including 1735 lowincome, multiethnic inner-city women at high risk for PNDS (low income and mainly having a high school or lower educational level). In that sample, the mean age and the number of primipara were much lower than those of the present sample, thereby enhancing the dimension of the risk for PNDS. They evaluated women once prenatally (mean gestational age 15.1 weeks) and three times postpartum (3, 11 and 25 months) using the CES-D (considering depressive symptomatology as significant if CES-D scores ever ≥16). Using the same type of statistical analysis as in the present work, they found 5 different evolutionary trajectories of PNDS. A group “never” depressed (71%), a group depressed only antenatally (“antepartum”, 6%), a group slightly depressed antenatally reaching higher levels of depressive symptoms at 4 months postpartum and recovering around 18 months (“postpartum”, 9%), a group of women depressed throughout the follow-up (“chronicle”, 7%) and a group depressed from one year postpartum (“late”, 7%). In the study by Mora et al., as in the present one, the “never” depressed groups accounted for about 70% of the sample, suggesting that, whatever the SES, the perinatal period does not significantly influence the mood of approximately three-quarters of women. In the present study, the “post-partum” group had an evolutionary profile that was comparable to that of the group “postpartum” in the study by Mora et al., except with regard to the intensity of symptoms (maximum CES-D scores: present study 15 vs about 30 in Mora's study). This suggests that a subgroup of new mothers presents with a higher rate of depressive

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symptoms during the first months postpartum. As the CES-D scores in this group did not reach clinical significance in the present study, and as it was the only one for which the intensity of symptoms was very different from that in Mora's groups, we hypothesized that the intensity of depressive symptoms in this profile could be particularly influenced by low SES. The “chronic” sub-groups of the two studies presented with high CES-D scores (average CES-D score about 27). Finally, our “antepartum” subgroup accounted for 21% of the sample and the CES-D scores remained clinically significant throughout the follow-up, whereas Mora's “antepartum” sub-group accounted for only 6% of their population, with nonclinically significant scores from 4 months post-partum. The slight increase in the intensity of symptoms in our “antepartum” sub-group at the end of follow-up perhaps reflects a late onset of depressive symptoms among some women, although the size of this sample does not make it possible to define a “late” subgroup. The late onset or secondary increase in depressive symptoms after one year post-partum could reflect depressive symptoms related to a subsequent pregnancy, because none of the two studies took into account the occurrence of another pregnancy during the follow-up period. In what concerns risk factors for each trajectory, past personal history of self-reported depressive episodes, which is generally recognized as a risk factor for perinatal depressive symptoms (Beck, 2001; Micali et al., 2010) does not seem to influence any of the trajectories of depressives symptoms in the present study. Nevertheless, PNDS risk factor studies mostly compare depressed versus non-depressed women cross-sectionally. In the present work, considering depressive symptoms according to evolutionary trajectories from pregnancy to late postpartum led to studying relatively small sub-groups, especially the chronic sub-group with 16 patients, which may have decreased the power of the analysis. In the present study, the “antepartum group”, i.e. the largest with clinically significant CES-D scores, was the only one for which analysis showed several significant risk factors for PNDS. Since most of these variables are kinds of socioeconomic vulnerabilities (income, parity), this finding suggests that socioeconomic factors might influence the clinical significance of depressive symptoms even in a high SES sample. Moreover, previous evidence largely suggests that individuals with low SES have higher levels of depressive symptoms and depressive disorders. The evidence seems the most consistent when income or composite measures of SES are compared, as opposed to educational measures, although this pattern is by no means conclusive. As suggested in other studies (Hobfoll, 2002), low SES could precede the development of depressive symptoms or disorders by creating disproportionate levels of negative emotions and attitudes. Indeed, several studies indicate that individuals with low SES more frequently encounter negative life events and chronic stressors (Murrell and Norris, 1991; Stansfeld et al., 1998), which, in turn, have a direct negative impact on emotional experiences (Stansfeld et al., 1995). On the other hand, trait anxiety was the only factor influencing the two groups remaining symptomatic throughout the follow-up (“antepartum” and “chronic”). This result is concordant with that of a preceding study showing that women with anxiety disorders during pregnancy had a higher risk of presenting with intense postnatal depressive symptoms (Sutter-Dallay et al., 2004). The fact that anxiety traits levels are risk factors for being in one of the two sub-

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groups with clinically significant CES-D scores is also in keeping with other studies showing strong links between anxiety and long-term depression (Hölzel et al., 2011). The selection bias concerning this sample, which was underlined in preceding publications (Sutter et al., 2003; Sutter-Dallay et al., 2004, 2011; Verdoux et al., 2002) regarding the high inclusion of women of middle–high SES and education level does not concern the present work, which is “based” on this bias. Other limitations should be taken into account when interpreting the findings. As already underlined, the results were obtained in a fairly small sample and some of the identified trajectory groups are small. Consequently, the descriptive values and estimations are affected by group size. On the other hand, the greater number of evaluations during the follow-up means that the trajectories of the different groups of women can be more carefully defined. 5. Conclusions The present findings underline that perinatal depression cannot be considered anymore as a homogenous entity, since about four or more different evolutionary profiles are distinguishable. More specifically, the main interest of the present study is to highlight that, whatever the socioeconomic status at inclusion, different comparable evolutive profiles of PNDS exist from pregnancy to late postpartum. Furthermore, the present findings suggest that these different profiles are influenced by environmental variables, in particular by socioeconomic characteristics such as income or parity. Role of funding sources This study was financially supported by a grant from the French Ministry of Health (“Programme Hospitalier de Recherche Clinique-1995”) and by a grant from SmithKline-Beecham Laboratories. They had no further role in the study design, in the collection, analysis, interpretation of the data, writing of the paper, and in the decision to submit the paper for publication. Conflict of interest All authors declare that they have no conflicts of interest. Acknowledgments We acknowledge J.F. Dartigues, B. Dubroca, A. Cantagrel who helped to organize the survey, F. Laoudj for her assistance with data processing. We are most grateful to the research psychologists who collected the data, and to the obstetricians and the midwives who helped in the recruitment, especially D. Dallay, D. Roux, J.J. Leng, and J. Horovitz. We also thank Ray Cooke who kindly reviewed the language of this paper.

Appendix 1 Regarding selection of the number of groups, we used four criteria. We used Jeffrey's criterion of choice model (Jeffreys, 1961) to examine the relative credibility of the different models according to the data. We then compared iteratively the value of BIC for a model of n groups with the previous (n − 1 groups) and next (n + 1 group). At the same time, we analyzed the average probability of belonging to each group (average posterior probability) by considering a threshold of .70 (Nagin, 2005). Finally, the number of subjects in each group and the relevance of the theoretical solutions also governed the chosen solution. Shapes of trajectories were based on the polynomial model best fitting the observations. By comparing the value of BIC and following the recommendations of

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