New Parents and Mental Disorders: Title and subTitle BreakA Population-Based Register Study FREE

Postpartum depression is a serious mental health problem for women and their families,¹ with an estimated prevalence of about 10% to 15% among mothers.^{2 - 3} Postpartum mental disorders also include more severe postpartum psychoses with a prevalence of about 1 per 1000 births.^{4 - 5} Such episodes require close attention, often including hospitalization, both because of the severity of symptoms and because these conditions are potentially life-threatening to both the woman and her newborn child.⁶ Previous studies have identified primiparity as a risk factor for postpartum psychoses,^{7 - 10} and Kendell et al⁴ pointed out that the increased risk among primiparous women could not be attributed to the avoidance of further pregnancies by mothers who had a puerperal psychosis after their first birth.

Although the impact of childbearing differs between men and women, becoming a father is a major change that reasonably could be thought to affect the mental health of men. Paternal “postpartum” mood disturbance and other mental disorders have been assumed to be rare¹¹ and have not, until recently, attracted much attention. There is some indication that a small percentage of men experience postpartum depressive symptoms.^{12 - 14} A study by Ramchandani et al¹⁵ showed that 4% of the fathers examined had depression 8 weeks after childbirth, but the men were not compared with a control group, making it uncertain whether their morbidity exceeds that among nonfathers.¹⁶ Studies have mainly focused on prevalence of depressive symptoms and have not established whether fathers experienced first onset of depression during the postpartum period or if the men had recurrence of symptoms and a previous diagnosis of a mental disorder.¹⁷ The possible relationship between becoming a father and first onset of mental disorders has therefore still not been established.

The concept of postpartum mental disorders is usually confined to disorders with onset during the first 6 weeks after childbirth in the International Statistical Classification of Diseases, 10th Revision (ICD-10)¹⁸ or 4 weeks in the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV), with the qualifier limited to specific diagnoses.¹⁹ It has been suggested, however, that postnatal depression is a reflection of the burden of child rearing rather than childbearing,⁹ which could lead to the expectation that the increased risk of postpartum mental disorders extends well beyond 6 weeks after becoming a parent.

Finally, one could hypothesize that premorbid psychological traits or other risk factors for mental disorders affect the chance of becoming a parent as well as the age at which one becomes a parent for the first time. If this is the case, the task of choosing a valid comparison group becomes more complex, but this dynamic population process of “selection into parenthood” has generally not been addressed directly in studies of postpartum mental disorders.

Consequently, the aim of this study was to estimate the risk of postpartum mental disorders necessitating hospital admission or outpatient contact for fathers as well as mothers. We chose to include a 1-year postnatal follow-up period after the birth of a first live-born child, and, finally, we investigated if parents in general differed from nonparents in the risk of admission for a mental disorder and how this difference varied with age.

We used data from the Danish Civil Registration System (CRS)²⁰ to obtain a large and representative set of data on Danish persons. Among many other variables, it includes the CRS number, sex, date of birth, continuously updated information on vital status, and CRS number of parents. It contains complete information on all children, thus ensuring that all firstborn children of the study population are identified. The CRS number is used as a personal identifier in all national registers, enabling accurate linkage between and within registers (eg, linking parents with children).²⁰

Our study population included all persons born in Denmark between January 1, 1955, and July 1, 1990, who were alive at their 15th birthday (N = 2 357 942).

The study population was linked with the Danish Psychiatric Central Register,²¹ which was computerized in 1969. The Danish Psychiatric Central Register contains data on all admissions to Danish psychiatric inpatient facilities and, at present, includes data on approximately 600 000 persons and 1.6 million admissions. There are no private psychiatric inpatient facilities in Denmark, ensuring that all admissions are represented in the register. From 1995 onward, information on outpatient visits to psychiatric departments was included in the register. From 1969 to 1993, the diagnostic system used was the Danish adaptation of the International Classification of Diseases, Eighth Revision (ICD-8)²² and from 1994, the ICD-10.¹⁸

Separate analyses were conducted for the following mental disorders: (1) all diagnoses combined; (2) schizophrenia, schizotypal and delusional disorders (ICD-8: 295.XX, 297.XX, 298.39, 301.83; ICD-10: F20-F29); (3) unipolar depressive disorders (ICD-8: 296.09, 269.29, 296.89, 296.99, 298.09, 300.49, 301.1; ICD-10: F32, F33, F34.1, F38.8, F39.0); (4) bipolar affective disorders (ICD-8: 296.19, 296.39, 298.19; ICD-10: F30, F31, F34.0, F38.0); (5) adjustment disorders (ICD-8: 307, 308.4; ICD-10: F43); (6) puerperal disorders not elsewhere classified (ICD-8: 294.49; ICD-10: F53), and (7) other remaining diagnoses in ICD-8 and ICD-10. Cohort members were classified with each of the above disorders if they had been admitted to a psychiatric hospital with a diagnosis of the disorder. The time of onset was defined as the date of the first psychiatric admission related to the disorder.

Additional analyses were made for outpatients with all diagnoses combined. The time of onset was defined as the date of first outpatient contact. Information on this outcome was available from 1995 to 2005.

A total of 2 357 942 cohort members were followed up from their 15th birthday or January 1, 1973, whichever came later, until date of onset of the disorder in question, date of death, date of emigration from Denmark, or July 1, 2005, whichever came first. For the outpatient analyses, cohort members were censored at the time of first psychiatric admission. Time since birth was treated as a time-dependent variable measuring time since the birth of a first live-born child (singletons only). Furthermore, the pregnancy period was included, but pregnancies ending in abortion (both elective abortions and miscarriages) were not included in the study. Variables were categorized as a pregnancy period from 270 to 0 days before birth, and after childbirth as 0 to 9, 10 to 19, or 20 to 29 completed days or 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or 11 completed months. For analyses of time since birth, we only considered the period from birth to 12 months after the birth, date of birth of a sibling, or death of first child, whichever came first.

The study was designed as a cohort study and data were analyzed in a survival analysis using log-linear Poisson regression,²³ with the logarithm of person-years as an offset variable in the SAS GENMOD, version 9.1, procedures (SAS Institute Inc, Cary, NC). This method approximates a Cox regression when analyzing large data sets.^{23 - 24}

All relative risks (RRs) were adjusted for calendar period (1-year groups) and age (1-year groups), and separate analyses were performed for each sex. Age, calendar period, parenthood, and time since birth were treated as time-dependent variables.²⁵ All P values were based on likelihood ratio tests (P<.05 was considered statistically significant), and 95% confidence intervals (CIs) were calculated by Wald test.

This study was approved by the Danish Data Protection Agency.

From 1973 to 2005, a total of 630 373 women and 547 431 men became parents for the first time, and during the first year after childbirth these parents contributed 1 115 639 person-years at risk. A total of 1171 women and 658 men were admitted with a mental disorder to a psychiatric hospital during the first 12 months after parenthood (first-time admissions; Table 1), and the corresponding prevalence of severe mental disorders through the first 3 months after childbirth was 1.03 per 1000 births for mothers and 0.37 per 1000 births for fathers.

For primiparous women, the first weeks and months after the delivery were associated with an increased risk of first admission with any mental disorder (Table 1), and the period from 10 to 19 days postpartum was associated with the highest risk (RR, 7.31; 95% CI, 5.44-9.81) compared with women who had given birth 11 to 12 months prior (reference group). The increased risk of admission among mothers remained statistically significant through the first 3 months after childbirth regardless of age of the mother.

Additional analyses (not shown) indicated that for women giving birth to their second live-born child, the increased risk of postpartum mental disorders was still present but was reduced compared with primiparous women, and after the birth of a third child, no association between time since birth and mental disorders was found.

Fathers had a notably different risk pattern than mothers: no temporal trends between childbirth and mental disorders were found (Table 1). No period either during their partner's pregnancy or during the first 0 to 12 months after first-time parenthood was associated with increased risk of first-time hospital admission for a mental disorder. On the contrary, results showed a slightly decreased risk of admission with any disorder during the first weeks after childbirth, although it was only statistically significant 10 to 19 days postpartum compared with men who became fathers 11 to 12 months prior (RR, 0.50; 95% CI, 0.26-0.95).

Separate analyses were done for the different diagnostic categories studied. For mothers, the increased risk of admission with unipolar disorders persisted through the first 5 months postpartum but only up to 30 days postpartum for schizophrenia-like disorders and through 2 months postpartum for bipolar affective disorders (Table 2). Diagnosis-specific risks of hospital admission among fathers showed no significantly increased risk of admission in any of the groups analyzed (results not shown).

We assumed that parents admitted to a hospital with a mental disorder during the postpartum period would represent the most severe cases. Additional analyses were performed in which first outpatient contacts were used as the outcome of interest (1369 mothers and 664 fathers). This included a group of patients with postpartum mental disorders that were not as severe as the disorders necessitating admission.

For mothers, a temporal association with increased risk of outpatient contact and time since childbirth was found, although it was not as high as the risk of hospital admission (Table 3). Findings were similar to those related to admission: the period related to the highest RR of having an outpatient contact was 10 to 19 days postpartum (RR, 2.67; 95% CI, 1.99-3.59) compared with mothers having a child 11 to 12 months prior, and the risk of outpatient contact during pregnancy was decreased compared with the period after childbirth. First-time fatherhood was not associated with any increased risk of having an outpatient contact during the first 12 months after the birth of a child.

Mothers, but not fathers, had an increased risk of hospital admission for postpartum mental disorders (first-time admissions and outpatient contact) through the first 3 months after the birth of a first live-born child. We wanted to investigate if there was an overall risk of mental disorders associated with parenthood, regardless of time since birth of the child. Further age-specific analyses were made comparing risks of admission among parents vs nonparents, which was a dynamic group consisting of “never parents” and future parents. Results indicated that both men and women aged up to about 26 years had an increased risk of hospital admission if they had become parents compared with nonparents of the same age (Figure). This pattern changed with increasing age: risks of admission were higher among nonparents (men and women) starting at about age 30 years compared with parents of the same age (Figure).

Results in Table 1 and Table 3 showed that new mothers had an increased risk of admission/outpatient contact with a mental disorder during the first few months after childbirth compared with mothers who gave birth 11 to 12 months prior. Since parents and nonparents have a significantly different incidence of admission, as shown in the Figure, results are also presented for risk of admission (Table 4) and outpatient contact (Table 5) for new parents with nonparents as a reference group. These results show the effect of parenthood on mothers and fathers compared with nonparents. As with the other results, the period with the highest risk of admission was 10 to 19 days postpartum for mothers (RR, 4.14; 95% CI, 3.54-4.83) (Table 4), with the risks significantly increased up to 2 months postpartum compared with nonmothers; this was also true for outpatient contacts (Table 5). New fathers had a decreased risk of admission and outpatient contact compared with nonfathers (Table 4 and Table 5).

Our results show a temporal association for women, with an increased risk of psychiatric hospital admission for any severe mental disorder from 0 to 3 completed months after birth of first live-born child, after adjusting for mothers' age, compared with mothers 11 to 12 months postpartum. The risk was also increased for psychiatric outpatient contacts, although it was not as elevated as the risk of admission. In contrast, the pregnancy period was associated with a decreased risk of admission or outpatient contacts. For mothers, diagnosis-specific analyses showed an increased risk of admission for unipolar depressive disorder through the first 5 months postpartum and 1 month postpartum for schizophrenia-like disorders and 2 months postpartum for bipolar affective disorders.

In contrast, fatherhood was not associated with any increased risk of admission or outpatient contact.

Overall, men and women who did not become parents during the study period had a different risk pattern than parents: young nonparents (ie, younger than about 25 years) had a lower incidence of admission with a mental disorder, whereas older nonparents had a higher incidence of admission compared with parents of the same age. Individuals who became parents between ages 25 and 30 years (the age range of the majority of first-time parents in Denmark) had similar rates of psychiatric contacts as nonparents of the same age.

In the current study, prevalence of admission for primiparous women was 1.03 per 1000 births through the first 3 months after childbirth, similar to the prevalence found by Kendell et al⁴ in their study on puerperal psychoses in Scotland. However, their study included a smaller group of patients than the present study, and the women served as their own controls from 2 years before childbirth. Kendell et al found that the pregnancy period was protective of onset of psychotic symptoms. Similarly, we found that pregnancy seemed to be protective of admission to a psychiatric hospital in mothers (RR, 0.53; 95% CI, 0.40-0.70). It should be noted, however, that this does not necessarily apply to all pregnant women, as we were able to study only pregnancies leading to a live-born child.

In the study by Ramchandani et al,¹⁵ 4% of fathers experienced symptoms of depression 8 weeks postpartum. Our results add further to this finding because more than 600 men were admitted during the observation period and fatherhood per se does not prevent severe mental disorders in men. Our data argue against any temporal association between fatherhood and mental disorders, since no aggregation in incidence of mental disorders was found during the period of 0 to 12 months after birth of a first child in a group of men never previously admitted to a psychiatric hospital. We believe that this result challenges the concept of severe paternal postpartum mental disorder.

There was no association between time since becoming a father and risk of mental disorders as measured by admissions to a psychiatric hospital or outpatient contact. This may indicate that the causes of postpartum mental disorders are more strongly linked to an altered physiological process related to pregnancy and childbirth than psychosocial aspects of motherhood. This is in line with the findings from Bloch et al,²⁶ who provided direct evidence that reproductive hormones were involved in the development of postpartum depression and suggested that women with a history of postpartum depression were differentially sensitive to their mood-destabilizing effects. Our results could also reflect that mothers generally are more involved in the child-rearing process, especially initially, with the demands of breastfeeding and sleep deprivation, and that this dramatic change in lifestyle accompanying the birth of a child is more of a precipitant for mental disorders in women than in men. Furthermore, our results could indicate that fathers are less likely to seek care compared with women.

Both women and men who had not become parents during the study period had a lower risk of hospital admission for a mental disorder up to age 25 years compared with parents at the same age during the study period, as measured by incidence per 10 000 person-years. Contrary to this, older nonparents (≥30 years) had an increased incidence of admission with a mental disorder compared with parents of the same age. Diverse mechanisms are likely to explain these differences. First, parents may be a selected segment of the population with respect to overall risk of mental disorders. Second, risk of admission for both parents and nonparents changed at about the age range of the majority of first-time parents in Denmark. This could indicate that women and men who become parents very early in their lives may represent lifestyles that are different from the majority and that these findings could be explained by a selection phenomenon associated with psychopathology or risk factors for mental disorders. This is also likely to be the case with older nonparents. We believe that our results demonstrate interactions (effect modification) between parenthood and age and the overall risk of admission for severe mental disorders because not only is the risk of admission different between parents and nonparents, but the difference is highly dependent on the age of the persons examined. Because of this complex age-dependent discrepancy between the dynamic groups of parents (not taking time since birth of child into account) and nonparents (never parents and future parents), it is particularly important to choose a reference group among other mothers and fathers when studying the impact of childbirth on parents' mental health.

Accurate estimates of the rates of and risk factors for postpartum depression are highly important for the scientific and clinical understanding of mental and behavioral disorders during the postpartum period as well as for planning mental health services for childbearing women and their families.³ There has been a large variation in the reported prevalence in studies of both maternal and paternal postpartum mental disorders, which might be caused by differences in the timing of assessment or by discrepancies in measures of incidence and prevalence.^{2 ,27} Heightened public awareness may make it appear that the prevalence of postpartum mental depression is increasing.²⁸ In our population-based register study, we were able (for the first time in men) to make specific analyses on incident cases only, since all admissions to psychiatric hospitals in Denmark are recorded. Unlike many studies, we used a broad definition of postpartum mental disorders including all diagnoses, since the range of disorders is wide¹ and postpartum mental disorders are distinguished by their timing and not by their phenomena.² We combined this with a 12-month follow-up period to produce a complete picture of mental disorders during this period.

Regarding mothers, our results indicate that an observation time of at least 3 completed months postpartum is necessary in the study of hospital admission for moderate and severe mental disorders and 5 months when studying unipolar depression only. Furthermore, in studies of postpartum mental disorders, choice of reference groups should be considered because baseline rates of admission for mental disorders depend on parenthood in general, as we showed in Table 1 and Table 3 compared with Table 4 and Table 5. Terp and Mortensen⁵ also used Danish registers in their study of postpartum psychoses, but their control group was the general female background population, including nonmothers, during a 3-month study period. Consequently, those authors found lower risks associated with admission during the postpartum period than in our study.

In the DSM-IV and the ICD-10, specific diagnoses for puerperal mental disorders are limited to an onset within 6 weeks (ICD-10) or 4 weeks postpartum (DSM-IV).^{18 - 19} A total of 119 women had the diagnostic codes 294.4 (ICD-8) and F53.X (ICD-10), indicating a mental and behavioral disorder associated with the puerperium, not elsewhere classified. Results showed a large variance in these ICD-8 and ICD-10 diagnoses, but by adjusting for calendar period in the statistical analysis, we took this skewed distribution into consideration. The relatively large number of women with these diagnoses could be explained by clinicians' reluctance to diagnose patients as having more specific disorders perceived to be more severe or stigmatizing.

Our study included first-time parents and risk of first-time admission or outpatient contact. It is estimated that about 40% to 50% of all cases with postnatal depression episodes go undetected,^{29 - 30} and mothers admitted with an affective disorder represent the most severe cases. Consequently, our results regarding risk of postpartum mental disorders are an underestimate. We had no access to information on possible symptoms of depression not necessitating admission or outpatient treatment in a psychiatric clinic. Furthermore, information on potential confounders, such as race/ethnicity or socioeconomic status, was not available.

Primiparity is a risk factor for postpartum mental disorders in mothers^{4 ,7 - 8} but has not received attention in studies on fathers.¹⁷ In the current study, only results regarding women and men having their first live-born child (singletons only) were assessed, and these results cannot be converted into risk of postpartum mental disorders for multiparous women and their partners.

We documented the strong temporal association between childbirth and prevalence of severe mental disorders among primiparous women, for both first-time hospital admissions and outpatient contacts, but we did not find any indication of such an association among men who become fathers. Men who do become fathers are, of course, not protected against developing mental disorders; hence, fatherhood and mental disorders will co-occur. Our results, however, do not support fatherhood as a specific risk factor for severe mental disorder and challenge the concept of severe paternal postpartum mental disorder.