I had a miscarriage.

[rainous]

It was during that period that I became pregnant but in less than 3 weeks, I had a miscarriage.

How does the sentence look, in terms of brevity?

[Raymott]

It was during that period that I became pregnant but in less than 3 weeks, I had a miscarriage.

How does the sentence look, in terms of brevity?

If you want the sentence to reflect the brevity of the pregnancy, (for artistic or other reasons) you could write, "Around then, I [also] had a 3-week miscarriage." And then don't mention it again. Mentioning such a usually distressing event in so cursory a way would be a good way to illustrate how miserable a time you were going through.
It would generally be unnecessary to point out that you got pregnant since this is necessary for you to have a miscarriage.

[emsr2d2]

I think Raymott meant "Around then, ..." not "Around them, ..."

[Raymott]

I think Raymott meant "Around then, ..." not "Around them, ..."

Thanks, I've changed it.

[JohnParis]

Hi Rainous

"in terms of brevity"?

If it's brevity you're looking for, would you consider:

That's when I became pregnant, but I miscarried in less than three weeks. (14 words versus your original 19)

"It was during that period" refers back to a period of time that was probably mentioned in a (or the) previous sentence. So, there is no point in saying any more than "That's when" because it succinctly refers to the period previously mentioned.

[Raymott]

Hi Rainous

"in terms of brevity"?

If it's brevity you're looking for, would you consider:

That's when I became pregnant, but I miscarried in less than three weeks. (14 words versus your original 19)

"It was during that period" refers back to a period of time that was probably mentioned in a (or the) previous sentence. So, there is no point in saying any more than "That's when" because it succinctly refers to the period previously mentioned.

How does your 14 beat my 8?

[rainous]

Thank you both for whipping up such tasteful sentences out of thin air.
I don't know when I will ever be able to write sentences like that on my own.

At first, I was blown away by Raymott's hard-boiled Hemingway style but now that I have seen John's more-than-adequate (Does this phrase make sense?) version, I am seriously torn between the two.

I think I will use both in my writing since I am sure I will have to mention the miscarriage a couple of more times somewhere further along the line.

Thanks again.

[JohnParis]

How does your 14 beat my 8?

It doesn't.
You get the gold star.