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There are not much chances of getting pregnant .Sometimes the periods may be delayed due to stress
There are very less chances of getting pregnant just before onset of menses. The stomach pain and vomiting
are not the definite signs of pregnancy
.If the periods are delayed for more than a week then go for a urine pregnancy test.
Hopefully she will be fine.
Hope this answers your query. If you have additional questions or follow up queries then please do not hesitate in writing to us. I will be happy to answer your queries.
Wishing you good health.