Pregnancy often equals a postpartum mother who worries (rightly or wrong) about her now perceived weight gain...so the ad companies take a shot at sending all new mothers these targeted ads.
One aspect of using the 'Net many folks don't realize is your browser brings back "3rd party" assets: including 'tracking cookies', which follow and report your movements across the 'Net: then Ad agencies compile your behavior (a profile of you) to then send ads back at you.
You must modify your browsers 'automatic' behavior so it restricts what gets returned, for both security and privacy.
Get Firefox as your default browser & use it for everyday tasks.
The following mods help, but methods ("vectors") are dynamic, and users must stay abreast of daily threats.
FIREFOX: Tools> Options> Privacy> top drop menu set to "Firefox will use custom settings..."> Check 'Accept Cookies from sites'
►Un-Check 'Accept 3rd Party cookies'.
A good collection of effective add-on's (Official Mozilla) is here:
https://addons.mozilla.org/collections/dunbar-pappy/dunbarpappy/
AdBlock Plus (with 'subscription' added) & "Better Privacy" also help defray rubbish.
►► At minimum, get the #1 item for malware prevention: "NoScript", which constrains automagically fetching & deployment of potentially tainted assets.
[Bookmark and refer to this page for how it works, and how to use it...very straight forward; http://noscript.net/features#contentblocking
INTERNET EXPLORER does not handle 3rd party assets very well (or anything else) and won't give nearly the control as Firefox.
It is garbage.
Use at your own demise.
Targeted advertising "Opt out" sign in pages;
Google here: http://www.google.com/privacy_ads.html
Yahoo: http://info.yahoo.com/privacy/us/yahoo/opt_out/targeting/details.html
NAI garbage: http://www.networkadvertising.org/managing/opt_out.asp#