Is Trimethoprim safe at 35 weeks of pregnancy?

Question

Hi doctor,

I am almost 35 weeks pregnant, and I had minor period-like cramps and went to the GP. They tested my urine, saw that it was dark, and that the dipstick showed bacteria. They prescribed an antibiotic, Sulfamethoxazole and Trimethoprim, for ten days, and I have not started the course as I am scared of adverse effects for my baby.

Please help.

Thank you.

Answer 1

Hi,

Welcome to icliniq.com.

I am deeply concerned about your worries.

I completely understand why you paused before starting it. When you are 35 weeks pregnant, every medication feels scary.

Let us break this down clearly: You are almost 35 weeks. Urine dipsticks showed bacteria. But you also said the lab culture showed no growth.

A dipstick can suggest infection, but urine culture is the gold standard. If the culture truly showed no growth, that means no confirmed bacterial infection.

Now, about the medication, Sulfamethoxazole and Trimethoprim are commonly known as Trimethoprim-Sulfamethoxazole. In the late third trimester, this medication is generally avoided if possible because:

Trimethoprim affects folate metabolism.
Sulfonamides near delivery can increase the theoretical risk of newborn jaundice.
It is sometimes used in pregnancy if necessary, but at 35 weeks, it is not usually the first choice unless there is a strong reason.

For urinary infections in late pregnancy, safer, commonly used options are:

Cephalexin.
Amoxicillin.
Nitrofurantoin is used in certain cases, but is usually avoided very near delivery.

Now the key issue is if your culture shows no growth, and you do not have fever, burning urine, severe lower abdominal pain, or back pain with fever. Then this may not be a true UTI (urinary tract infection). Dark urine alone can mean dehydration or concentrated urine. Minor cramping at 35 weeks can also be Braxton Hicks contractions or uterine stretching.

Here is what I suggest:

Call your GP (general practitioner) and clarify whether the urine culture is truly negative. If yes, ask whether antibiotics are still necessary. Ask if a repeat urine sample should be done.
Do not start the antibiotic until you clarify, unless you develop fever, painful urination, severe pelvic pain, and reduced baby movements.

Right now, based on what you told me, this does not sound like a confirmed infection. Answer these:

Do you feel burning when you pee?
Any fever?
Any back pain on one side?
Is the baby moving normally?

You are doing the right thing by questioning before taking medication in late pregnancy.

Let us make sure it is truly needed first.

I hope you are satisfied with my answer.

For further queries, you can consult me at iCliniq.

Best wishes.