Reviewer’s report
Title: 
A rise in births following contraceptive failure in France between 2010
and 2016: results from the French national perinatal surveys
Version: 
0 
Date: 
10 Jun 2020
Reviewer: 
John Cleland
Reviewer's report:
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This is an intriguing analysis that shows a rise between 2010 and 2016 in the
proportion of live births that are a consequence of reported contraceptive failure.
Following the 2012 pill scare in France, the contraceptive method-mix shifted
away from pills to greater use of condoms and other methods. But surprisingly
this shift does not explain the increase in the contribution of failure to live births.
Instead the reason is rises in reported failure among women using pills and
condoms. A plausible explanation exists for condom users. Couples switching
from pills to condoms may well experience a high failure rate; as noted in the
Discussion, failure tends to be higher in the initial months of use than
subsequently. The increase in pill failure is more puzzling. Indeed, one might
have expected the opposite, namely that women undeterred by the pill scare
might be more consistent users of this method. I suggest that the Discussion is
expanded slightly to take into account this point.
The paper is well written and the analysis is sound. I have only a few minor
points:
(1) In the abstract instead of "contraceptive failure leading to live births rose
from…", it might be clearer to say "the proportion of live births that were a
result of contraceptive failure rose from…"
(2) In Methods, a sharp increase between 2010 and 2016 in non-response
because of medical conditions, language difficulties or refusal is noted and this is
also acknowledged as a limitation in the Discussion. It would be helpful to
specify the contribution of refusal to this increase.
(3) In Table 2, the percent of IUD and implant+ users who claimed contraceptive
failure seems high in both surveys, in view of the high effectiveness of these
methods. It made me wonder about the validity of these self-reports. It must be a
temptation to blame a method for an unintended conception. This is another
potential limitation that merits a mention.
(4) In Table 3, I was struck that the increase in reported failure was remarkably
constant across socio-demographic sub-groups. This feature deserves a mention. 
Are the methods appropriate and well described?
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Yes
Does the work include the necessary controls?
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authors.
Yes
Are the conclusions drawn adequately supported by the data shown?
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Yes
Are you able to assess any statistics in the manuscript or would you
recommend an additional statistical review?
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require further assessment in your comments to the editors.
I am able to assess the statistics
Quality of written English
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Acceptable
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