Have you at any point handed in any consent forms to your doctors on what information you're happy for your doctor's to share with relatives ?

NAL, but sounds like a breach of NHS confidentiality policy (assuming it was NHS)

Complain to the practice - there will be someone there who deals specifically with confidentiality issues (often called the Caldicott Guardian). Of course, it may be helpful to have an idea of what you want from this, in mind. Clearly you can't undo the knowledge of the information, but for your own vindication you may want to ensure expectations are realistic. Do you want money, an apology, you want this person to lose their job, the entire practice to fall on their swords, your Mum to be banned from there, you want to change doctors etc. etc. I expect an apology at the very least, an acknowledgment this person needs a refresher course on patient confidentiality, and perhaps some monetary amount is probably what you're looking at here.

Time to write a formal complaint. Include as much detail as possible - especially who the receptionist was (a description if you don't know the name) Certainly include that you were intending to have a termination and that you were not going to tell your mother you're pregnant. If she has pro life views, include that too. PALS can help if needed. Obviously now she knows and you can't change that. What would you like the outcome to be, in an ideal scenario - formal apology, receptionist sacked, compensation, or something else?

You contact PALs (Patient Advice and Liaison Service) and put in a complaint. You also write a letter to the manager of the practice informing them of the breach in data protection and the distress it has caused you. You can inform them you have made a complaint to PALs

Phone and speak to the practice manager and make a formal complaint. That is a huge violation of privacy and breaks every rule about data protection

Did you ask your mum to go in and did she have permission to speak on your behalf previously?

As others have said, what do you want to get from this? The receptionist is only human, and slips of the tongue do happen. I'm not saying she wasn't wrong, she completely was. I recommend you lodge a complaint with the practice and suggest the receptionist gets some retraining so they don't make a similar mistake in the future with other's confidentials. There are training programmes on confidentiality, and how to deal with different situations in order to protect patient confidentiality.

Make a formal complaint with Patient Liaison. I would also have a conversation with your mum about boundaries - did you send her to enquire?

This is a clear breach of the Data Protection Act 2018. If you experience psychological suffering as a result of this breach you are entitled to seek compensation. The receptionist should be retrained re data protection and confidentially or sacked, depending on the policy of the GP surgery re breaches of medical information without consent. All surgeries have policies in place to deal with breaches.

Huge breach in confidentiality complain of course but just asking why send your mum in the first place as the prescription would be signed by the midwife and she would find out anyway.

The thing you need to ask yourself first is what kind of outcome would you actually like? This is clearly a breach of GDPR and medical ethics ~~but is not criminal~~. You could report it to the Information Commissioner's Office and they will be very interested. Medical stuff is a big no-no. You could approach the surgery manager directly with a formal letter asking why they are not training their staff and what they will be doing to remedy it. Obviously with the implication/threat that if you aren't happy you will raise it with the commissioner. They will of course deny any breach and you may be expected to provide evidence that you aren't simply being malicious.