Here is a Daily Mail story of a man who paid the ultimate price for not reading his travel insurance policy. You should always read the policy wording of your travel insurance cover or any other insurance you might take out. This is especially true when or cheap travel insurance premiums! Anyway here is the link to the Daily Mail Article; it really is tragic and quite callous on the part of the hospital.
Some insurers require you to declare any pre-existing conditions or treatments you may have had in the previous months or year/s and if you are unsure about part of the wording, you should always enquire before purchasing the policy. If you have a pre-existing condition or had treatments, its good practice to declare it to the insurer and get a written confirmation from them before buying.
Pregnancy is considered a pre-existing condition so be sure to check the policy-wording to ascertain as to how may weeks the policy cover is effective. Always read the policy wording every time you buy a policy because the cover, wording & excesses can always change.