The December 2011 peer-reviewed journal Family Relations reports the latest findings from the National Longitudinal Lesbian Family Study (NLLFS) on the well-being of children whose mothers split up before they were 17. The NLLFS has been following 85 children of lesbians born through donor insemination beginnning in the 1980's. Information about the study and its earlier published research is all located on the NLLFS website.
Of the 73 two-mother families in the study, 40 couples had split up by the time their child was 17 (over 90% of these occurred before the child was 13). This is a higher rate of separation than the divorce rate for married heterosexuals. 71% of separated couples reported shared custody of the children, a number considerably higher than the rate of shared custody among divorced heterosexuals. 59% of the couples had completed second-parent adoptions, and parents in that group were more likely to share custody. The children whose mothers had completed second parent adoptions were much more likely to report feeling close to both mothers. In 10 families, the birth mother was primary custodial parent. The study reports no families in which there was one primary custodial parent and that parent was the nonbiological mother.
The study's key finding: there was no difference in psychological health or problem behavior between those children whose mothers had completed second parent adoptions and those who had not, or between those whose mothers shared custody and those who did not. The authors note that this lack of association could reflect the small size of each subgroup. (Previous research from the NLLFS, published in Pediatrics, reported no difference in the well-being of children whose moms split up and those whose moms were still together.)
The study includes the information that 80% of the separations occurred before same-sex couples could enter civil unions in Vermont (July 2000), the first status available to same-sex couples that conferred the state-level legal consequences of marriage. Almost all occured before the couple could have entered marriage or its legal equivalent in the state where they lived. The study repeats this fact several times. In a footnote, the authors do note that marriage (or its legal equivalent) is neither necessary nor sufficient to confer legal parentage. Perhaps repetition of the fact of the unavailability of relationship recognition is designed to suggest that there could be variable outcomes for children whose parents marry and those who do not. While that is, of course, possible, if the data reported in this study holds it suggests otherwise. It takes a lot more time, effort, and money to complete a second parent adoption than to marry. A second parent adoption is also a strong statement of commitment to the child, as opposed to marriage which concerns the relationship of the women to each other. So if the children of second parent adoptions are no healthier or better adjusted than the children whose moms did not complete second parent adoptions, my hypothesis would be that the couple's marriage would produce no difference either.
One thing for sure -- there will be lots to research over the coming years, and the data from the NLLFS study will be the point of comparison for all that work.